adapted regular expression to correctly parse total coverage when using pytest-cov

> ----------- coverage: platform linux, python 3.6.6-final-0 -----------
> Name                      Stmts   Miss  Cover
> ---------------------------------------------
> integrade/__init__.py         0      0   100%
> integrade/api.py             86      0   100%
> integrade/config.py          36      1    97%
> integrade/exceptions.py       3      0   100%
> integrade/utils.py           11      0   100%
> tests/test_api.py           153      0   100%
> tests/test_config.py         46      0   100%
> tests/test_integrade.py       6      0   100%
> tests/test_utils.py          12      0   100%
> ---------------------------------------------
> TOTAL                       353      1    99%

issue: https://gitlab.com/gitlab-org/gitlab-ce/issues/48613