Bump coveralls from 1.9.2 to 1.11.1

Bumps [coveralls](https://github.com/coveralls-clients/coveralls-python) from 1.9.2 to 1.11.1.
- [Release notes](https://github.com/coveralls-clients/coveralls-python/releases)
- [Changelog](https://github.com/coveralls-clients/coveralls-python/blob/master/CHANGELOG.md)
- [Commits](TheKevJames/coveralls-python@1.9.2...1.11.1)

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

requirements_dev.txt

@@ -1,6 +1,6 @@
 black
 coverage==4.5.4
-coveralls==1.9.2
+coveralls==1.11.1
 flake8==3.7.9
 isort
 mock==3.0.5