Make typing introspection compatible with Python 3.7+

[motohedgehog]

This PR makes Nubia compatible with Python 3.7+ by taking into account the changes introduced by PEP 560. The implementation was heavily inspired by ilevkivskyi/typing_inspect project.

Also run TravisCI tests against Python 3.7.

Closes #2.

[motohedgehog]

Had to switch Travis distro to Xenial in order to get 3.7 (see travis-ci/travis-ci#9815).

[facebook-github-bot]

@ylectric has imported this pull request. If you are a Facebook employee, you can view this diff on Phabricator.

[codecov-io]

Codecov Report

Merging #37 into master will increase coverage by 0.09%.
The diff coverage is 88.5%.

@@            Coverage Diff             @@
##           master      #37      +/-   ##
==========================================
+ Coverage   65.45%   65.54%   +0.09%     
==========================================
  Files          29       30       +1     
  Lines        1731     1753      +22     
==========================================
+ Hits         1133     1149      +16     
- Misses        598      604       +6

Impacted Files	Coverage Δ
nubia/internal/helpers.py	75.94% <ø> (-2.32%)	⬇️
nubia/internal/typing/__init__.py	93.65% <100%> (ø)	⬆️
nubia/internal/typing/argparse.py	85.52% <100%> (ø)	⬆️
nubia/internal/typing/inspect.py	84.84% <84.84%> (ø)
nubia/internal/typing/builder.py	87.82% <87.17%> (-1.56%)	⬇️

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[motohedgehog]

At last :)

[facebook-github-bot]

@ylectric has imported this pull request. If you are a Facebook employee, you can view this diff on Phabricator.

[facebook-github-bot]

@ylectric has imported this pull request. If you are a Facebook employee, you can view this diff on Phabricator.

[facebook-github-bot]

@ylectric merged this pull request in 088e6f3.