Bump mock from 3.0.5 to 4.0.2

Bumps [mock](https://github.com/testing-cabal/mock) from 3.0.5 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@3.0.5...4.0.2)

Signed-off-by: dependabot-preview[bot] <[email protected]>

Author: dependabot-preview[bot]

requirements.txt

@@ -2,7 +2,7 @@ flake8==3.5.0
 Flask==1.0.2
 Flask-RESTful==0.3.7
 Jinja2==2.10.1
-mock==3.0.5
+mock==4.0.2
 pytest==4.5.0
 requests==2.22.0
 requests-mock==1.6.0