Ignore the unittest.mock warning in flake8

The flake8 check is warning that unittest.mock is not used. Add H216 to
disable the warning.

Author: m4dcoder

.flake8

@@ -1,5 +1,5 @@
 [flake8]
 max-line-length = 100
 enable-extensions = H203,H204,H205,H301,H303,H304,O101,O102
-ignore = E203,E402,W503
+ignore = H216,E203,E402,W503
 exclude=*.egg/*