Bump coverage from 4.3.1 to 4.5.1

Bumps [coverage](https://bitbucket.org/ned/coveragepy) from 4.3.1 to 4.5.1.
- [Changelog](https://bitbucket.org/ned/coveragepy/src/master/CHANGES.rst)
- [Commits](https://bitbucket.org/ned/coveragepy/branches/compare/coverage-4.5.1..coverage-4.3.1)

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

Author: dependabot-support

dev-requirements.txt

@@ -1,4 +1,4 @@
 pytest==3.2.5
-coverage==4.3.1
+coverage==4.5.1
 cython==0.27.3
 tox==2.5.0