Bump coveralls from 1.8.0 to 1.8.1

Bumps [coveralls](https://github.com/coveralls-clients/coveralls-python) from 1.8.0 to 1.8.1.
- [Release notes](https://github.com/coveralls-clients/coveralls-python/releases)
- [Changelog](https://github.com/coveralls-clients/coveralls-python/blob/master/CHANGELOG.md)
- [Commits](https://github.com/coveralls-clients/coveralls-python/compare/1.8.0...1.8.1)

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

setup.py

@@ -55,7 +55,7 @@ setup(
     extras_require={
         'dev': [
             'nose==1.3.7',
-            'coveralls==1.8.0',
+            'coveralls==1.8.1',
             'flake8==3.7.7',
             'xmlunittest==0.4.0'
         ]