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

Author: renovate[bot]

pyproject.toml

@@ -51,7 +51,7 @@ coveralls = [
     { version = ">=3.3.0", python = ">=3.5" },
     { version = "<2", python = "<3.5" },
 ]
-pytest-cov = "~2.8"
+pytest-cov = "~2.12.0"
 flake8 = ">=3.6.0"
 mock = "^3.0.5"
 bumpversion = "^0.5.0"