Bump pytest-cov from 2.6.1 to 2.7.1 (#70)

Bumps [pytest-cov](https://github.com/pytest-dev/pytest-cov) from 2.6.1 to 2.7.1.
- [Release notes](https://github.com/pytest-dev/pytest-cov/releases)
- [Changelog](https://github.com/pytest-dev/pytest-cov/blob/master/CHANGELOG.rst)
- [Commits](pytest-dev/pytest-cov@v2.6.1...v2.7.1)

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

Author: dependabot[bot]

poetry.lock

@@ -44,7 +44,7 @@ flake8-pyi = "^19.2"
 safety = "^1.8"
 
 pytest = "^4.4"
-pytest-cov = "^2.6"
+pytest-cov = "^2.7"
 pytest-randomly = "^3.0"
 
 sphinx = "^2.0"