build(deps): bump mock from 2.0.0 to 4.0.2 (#607)

Bumps [mock](https://github.com/testing-cabal/mock) from 2.0.0 to 4.0.2.
- [Release notes](https://github.com/testing-cabal/mock/releases)
- [Changelog](https://github.com/testing-cabal/mock/blob/master/CHANGELOG.rst)
- [Commits](https://github.com/testing-cabal/mock/compare/2.0.0...4.0.2)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>
Co-authored-by: dependabot-preview[bot] <27856297+dependabot-preview[bot]@users.noreply.github.com>

requirements.txt

@@ -21,7 +21,7 @@ pytest-cov==2.5.1
 # Rolling backport of unittest.mock for all Pythons
 # License: BSD
 # Upstream url: https://mock.readthedocs.io/en/latest/
-mock==2.0.0
+mock==4.0.2
 
 # Thin-wrapper around the mock package for easier use with py.test.
 # License: MIT