chore(deps): update dependency pytest-cov to ~2.12.0

Author: renovate[bot]

pyproject.toml

@@ -48,7 +48,7 @@ coverage = [
 coveralls = [
     { version = ">=3.3.0", python = ">=3.5" },
 ]
-pytest-cov = "~2.8"
+pytest-cov = "~2.12.0"
 flake8 = ">=3.6.0"
 mock = "^3.0.5"
 bumpversion = "^0.5.0"