chore(deps-dev): bump pytest-cov from 2.12.0 to 2.12.1 (#454)

Bumps [pytest-cov](https://github.com/pytest-dev/pytest-cov) from 2.12.0 to 2.12.1.
<details>
<summary>Changelog</summary>
<p><em>Sourced from <a href="https://github.com/pytest-dev/pytest-cov/blob/master/CHANGELOG.rst">pytest-cov's changelog</a>.</em></p>
<blockquote>
<h2>2.12.1 (2021-06-01)</h2>
<ul>
<li>Changed the <code>toml</code> requirement to be always be directly required (instead of being required through a coverage extra).
This fixes issues with pip-compile (<code>pip-tools#1300 &lt;https://github.com/jazzband/pip-tools/issues/1300&gt;</code><em>).
Contributed by Sorin Sbarnea in <code>[#472](pytest-dev/pytest-cov#472) &lt;https://github.com/pytest-dev/pytest-cov/pull/472&gt;</code></em>.</li>
<li>Documented <code>show_contexts</code>.
Contributed by Brian Rutledge in <code>[#473](pytest-dev/pytest-cov#473) &lt;https://github.com/pytest-dev/pytest-cov/pull/473&gt;</code>_.</li>
</ul>
</blockquote>
</details>
<details>
<summary>Commits</summary>
<ul>
<li><a href="https://github.com/pytest-dev/pytest-cov/commit/67d49b9e06cbc1cace3fc2cdfe70b09f55d1726f"><code>67d49b9</code></a> Bump version: 2.12.0 → 2.12.1</li>
<li><a href="https://github.com/pytest-dev/pytest-cov/commit/3685acbd61df9135e41b188374347d04d2d689db"><code>3685acb</code></a> Use 2019 image for pypy.</li>
<li><a href="https://github.com/pytest-dev/pytest-cov/commit/df20c973a5a34c4e085362dcf41df88fc3ee6297"><code>df20c97</code></a> Looks like I got the images wrong.</li>
<li><a href="https://github.com/pytest-dev/pytest-cov/commit/17252e0896ac18d7b15284d8dc4e2ecb16b050c9"><code>17252e0</code></a> Remove unnecessary pin.</li>
<li><a href="https://github.com/pytest-dev/pytest-cov/commit/ac7cc916268266807d43e9d7f0bcb1ae4277010c"><code>ac7cc91</code></a> Update changelog.</li>
<li><a href="https://github.com/pytest-dev/pytest-cov/commit/34edfa1cf80f8d722dec4f587b10d2783f89a0f0"><code>34edfa1</code></a> Avoid using toml as extra (<a href="https://github-redirect.dependabot.com/pytest-dev/pytest-cov/issues/472">#472</a>)</li>
<li><a href="https://github.com/pytest-dev/pytest-cov/commit/edc60bb9e560d7ea53056590a64a4e5c81b5e62c"><code>edc60bb</code></a> Document <code>show_contexts</code> (<a href="https://github-redirect.dependabot.com/pytest-dev/pytest-cov/issues/473">#473</a>)</li>
<li><a href="https://github.com/pytest-dev/pytest-cov/commit/297965e05a7712e50c2f8a4dc26cd189132aba22"><code>297965e</code></a> Update appveyor envs. Workaround pypy install problem.</li>
<li>See full diff in <a href="https://github.com/pytest-dev/pytest-cov/compare/v2.12.0...v2.12.1">compare view</a></li>
</ul>
</details>
<br />


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pyproject.toml

@@ -40,7 +40,7 @@ flake8-fixme = "^1.1.1"
 flake8-isort = "^4.0.0"
 flake8-variables-names = "^0.0.4"
 isort = "^5.8.0"
-pytest-cov = "^2.11.1"
+pytest-cov = "^2.12.1"
 pytest-mock = "^3.5.1"
 pdoc3 = "^0.9.2"
 pytest-asyncio = "^0.15.1"