Bump pytest-cov from 2.5.1 to 2.6.0 (#179)

Bumps [pytest-cov](https://github.com/pytest-dev/pytest-cov) from 2.5.1 to 2.6.0.
- [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@v2.5.1...v2.6.0)

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

setup.py

@@ -8,7 +8,7 @@
 folder = os.path.abspath(os.path.dirname(__file__))
 test_requirements = [
     'pytest==3.8.0',
-    'pytest-cov==2.5.1',
+    'pytest-cov==2.6.0',
     'pyquery==1.4.0',
     'requests_mock',
 ]