Update coverage from 4.4.2 to 4.5.1

Author: pyup-bot

requirements.txt

@@ -13,7 +13,7 @@ chardet==3.0.4
 click==6.7
 configparser==3.5.0
 cookiecutter==1.6.0
-coverage==4.4.2
+coverage==4.5.1
 cryptography==2.1.4
 docutils==0.14
 enum34==1.1.6