Update coverage from 5.1 to 5.3

Author: pyup-bot

setup.cfg

@@ -98,7 +98,7 @@ testing =
     jaraco.text>=3.1
 
     # measure test coverage
-    coverage==5.1; python_version != "3.4"
+    coverage==5.3; python_version != "3.4"
     coverage<5; python_version == "3.4"
     # send test coverage to codecov.io
     codecov==2.1.9