Bump mock from 3.0.4 to 3.0.5 (#353)

Bumps [mock](https://github.com/testing-cabal/mock) from 3.0.4 to 3.0.5.
- [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/3.0.4...3.0.5)

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

requirements/py27-tests.txt

@@ -1,4 +1,4 @@
-mock==3.0.4
+mock==3.0.5
 mozlog==4.0
 pyfxa==0.7.1
 pypom==2.2.0

requirements/py36-tests.txt

@@ -1,4 +1,4 @@
-mock==3.0.4
+mock==3.0.5
 pyfxa==0.7.1
 pypom==2.2.0
 pytest==4.4.2