Update coverage from 4.5.1 to 4.5.2

Author: pyup-bot

requirements.txt

@@ -2,7 +2,7 @@ pyyaml==3.13
 pytest==3.10.0
 pycodestyle==2.4.0
 argparse==1.4.0
-coverage==4.5.1
+coverage==4.5.2
 pytest-cov==2.6.0
 codeclimate-test-reporter==0.2.3
 codacy-coverage==1.3.11