Bump mock from 2.0.0 to 4.0.2

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](testing-cabal/mock@2.0.0...4.0.2)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

dev-requirements.txt

@@ -2,7 +2,7 @@
 
 blinker==1.4
 coverage==5.3
-mock==2.0.0; python_version == "2.7"
+mock==4.0.2; python_version == "2.7"
 pytest==6.1.2; python_version > "2.7"
 pytest<5.0; python_version == "2.7"
 pycodestyle==2.6.0