Scheduled monthly dependency update for February (#22)

### Update [pip](https://pypi.org/project/pip) from **18.1** to **19.0.1**.


<details>
  <summary>Changelog</summary>
  
  
   ### 19.0
   ```
   =================

Deprecations and Removals
-------------------------

- Deprecate support for Python 3.4 (`6106 &lt;https://github.com/pypa/pip/issues/6106&gt;`_)
- Start printing a warning for Python 2.7 to warn of impending Python 2.7 End-of-life and
  prompt users to start migrating to Python 3. (`6148 &lt;https://github.com/pypa/pip/issues/6148&gt;`_)
- Remove the deprecated ``--process-dependency-links`` option. (`6060 &lt;https://github.com/pypa/pip/issues/6060&gt;`_)
- Remove the deprecated SVN editable detection based on dependency links
  during freeze. (`5866 &lt;https://github.com/pypa/pip/issues/5866&gt;`_)

Features
--------

- Implement PEP 517 (allow projects to specify a build backend via pyproject.toml). (`5743 &lt;https://github.com/pypa/pip/issues/5743&gt;`_)
- Implement manylinux2010 platform tag support.  manylinux2010 is the successor
  to manylinux1.  It allows carefully compiled binary wheels to be installed
  on compatible Linux platforms. (`5008 &lt;https://github.com/pypa/pip/issues/5008&gt;`_)
- Improve build isolation: handle ``.pth`` files, so namespace packages are correctly supported under Python 3.2 and earlier. (`5656 &lt;https://github.com/pypa/pip/issues/5656&gt;`_)
- Include the package name in a freeze warning if the package is not installed. (`5943 &lt;https://github.com/pypa/pip/issues/5943&gt;`_)
- Warn when dropping an ``--[extra-]index-url`` value that points to an existing local directory. (`5827 &lt;https://github.com/pypa/pip/issues/5827&gt;`_)
- Prefix pip&#39;s ``--log`` file lines with their timestamp. (`6141 &lt;https://github.com/pypa/pip/issues/6141&gt;`_)

Bug Fixes
---------

- Avoid creating excessively long temporary paths when uninstalling packages. (`3055 &lt;https://github.com/pypa/pip/issues/3055&gt;`_)
- Redact the password from the URL in various log messages. (`4746 &lt;https://github.com/pypa/pip/issues/4746&gt;`_, `6124 &lt;https://github.com/pypa/pip/issues/6124&gt;`_)
- Avoid creating excessively long temporary paths when uninstalling packages. (`3055 &lt;https://github.com/pypa/pip/issues/3055&gt;`_)
- Avoid printing a stack trace when given an invalid requirement. (`5147 &lt;https://github.com/pypa/pip/issues/5147&gt;`_)
- Present 401 warning if username/password do not work for URL (`4833 &lt;https://github.com/pypa/pip/issues/4833&gt;`_)
- Handle ``requests.exceptions.RetryError`` raised in ``PackageFinder`` that was causing pip to fail silently when some indexes were unreachable. (`5270 &lt;https://github.com/pypa/pip/issues/5270&gt;`_, `5483 &lt;https://github.com/pypa/pip/issues/5483&gt;`_)
- Handle a broken stdout pipe more gracefully (e.g. when running ``pip list | head``). (`4170 &lt;https://github.com/pypa/pip/issues/4170&gt;`_)
- Fix crash from setting ``PIP_NO_CACHE_DIR=yes``. (`5385 &lt;https://github.com/pypa/pip/issues/5385&gt;`_)
- Fix crash from unparseable requirements when checking installed packages. (`5839 &lt;https://github.com/pypa/pip/issues/5839&gt;`_)
- Fix content type detection if a directory named like an archive is used as a package source. (`5838 &lt;https://github.com/pypa/pip/issues/5838&gt;`_)
- Fix listing of outdated packages that are not dependencies of installed packages in ``pip list --outdated --not-required`` (`5737 &lt;https://github.com/pypa/pip/issues/5737&gt;`_)
- Fix sorting ``TypeError`` in ``move_wheel_files()`` when installing some packages. (`5868 &lt;https://github.com/pypa/pip/issues/5868&gt;`_)
- Fix support for invoking pip using ``python src/pip ...``. (`5841 &lt;https://github.com/pypa/pip/issues/5841&gt;`_)
- Greatly reduce memory usage when installing wheels containing large files. (`5848 &lt;https://github.com/pypa/pip/issues/5848&gt;`_)
- Editable non-VCS installs now freeze as editable. (`5031 &lt;https://github.com/pypa/pip/issues/5031&gt;`_)
- Editable Git installs without a remote now freeze as editable. (`4759 &lt;https://github.com/pypa/pip/issues/4759&gt;`_)
- Canonicalize sdist file names so they can be matched to a canonicalized package name passed to ``pip install``. (`5870 &lt;https://github.com/pypa/pip/issues/5870&gt;`_)
- Properly decode special characters in SVN URL credentials. (`5968 &lt;https://github.com/pypa/pip/issues/5968&gt;`_)
- Make ``PIP_NO_CACHE_DIR`` disable the cache also for truthy values like ``&quot;true&quot;``, ``&quot;yes&quot;``, ``&quot;1&quot;``, etc. (`5735 &lt;https://github.com/pypa/pip/issues/5735&gt;`_)

Vendored Libraries
------------------

- Include license text of vendored 3rd party libraries. (`5213 &lt;https://github.com/pypa/pip/issues/5213&gt;`_)
- Update certifi to 2018.11.29
- Update colorama to 0.4.1
- Update distlib to 0.2.8
- Update idna to 2.8
- Update packaging to 19.0
- Update pep517 to 0.5.0
- Update pkg_resources to 40.6.3 (via setuptools)
- Update pyparsing to 2.3.1
- Update pytoml to 0.1.20
- Update requests to 2.21.0
- Update six to 1.12.0
- Update urllib3 to 1.24.1

Improved Documentation
----------------------

- Include the Vendoring Policy in the documentation. (`5958 &lt;https://github.com/pypa/pip/issues/5958&gt;`_)
- Add instructions for running pip from source to Development documentation. (`5949 &lt;https://github.com/pypa/pip/issues/5949&gt;`_)
- Remove references to removed ``egg=&lt;name&gt;-&lt;version&gt;`` functionality (`5888 &lt;https://github.com/pypa/pip/issues/5888&gt;`_)
- Fix omission of command name in HTML usage documentation (`5984 &lt;https://github.com/pypa/pip/issues/5984&gt;`_)
   ```
   
  
</details>


 

<details>
  <summary>Links</summary>
  
  - PyPI: https://pypi.org/project/pip
  - Changelog: https://pyup.io/changelogs/pip/
  - Homepage: https://pip.pypa.io/
</details>





### Update [tox](https://pypi.org/project/tox) from **3.6.1** to **3.7.0**.


*The bot wasn't able to find a changelog for this release. [Got an idea?](https://github.com/pyupio/changelogs/issues/new)*

<details>
  <summary>Links</summary>
  
  - PyPI: https://pypi.org/project/tox
  - Docs: https://tox.readthedocs.org/
</details>





### Update [PyYAML](https://pypi.org/project/PyYAML) from **4.2b1** to **4.2b4**.


*The bot wasn't able to find a changelog for this release. [Got an idea?](https://github.com/pyupio/changelogs/issues/new)*

<details>
  <summary>Links</summary>
  
  - PyPI: https://pypi.org/project/pyyaml
  - Homepage: http://pyyaml.org/wiki/PyYAML
</details>

requirements_dev.txt

@@ -1,13 +1,13 @@
-pip==18.1
+pip==19.0.1
 bumpversion==0.5.3
 wheel==0.32.3
 watchdog==0.9.0
 flake8>=2.6.0
-tox==3.6.1
+tox==3.7.0
 coverage==4.5.2
 Sphinx>=1.6
 cryptography>2.3
-PyYAML==4.2b1
+PyYAML==4.2b4
 requests>=2.7.0
 lxml>=1.3