Update mock requirement from ~=3.0.5 to ~=4.0.2

Updates the requirements on [mock](https://github.com/testing-cabal/mock) to permit the latest version.
- [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[bot] <support@github.com>

requirements.txt

@@ -1,5 +1,5 @@
 hjson~=3.0.1
-mock~=3.0.5
+mock~=4.0.2
 pyroute2==0.5.*
 pyserial~=3.4.0
 python-pppd==1.0.3