flake8 requirements: Update flake8-putty to 0.4.0

- Microsoft Windows filename selector fixes, with Appveyor CI testing
- Allow multiple codes to be disabled by per-line comments
- Allow comment after each rule line
- Prevent use with flake8 v3
- Support both pep8 and pycodestyle in test suite

misc/requirements/requirements-flake8.txt

@@ -9,7 +9,7 @@ flake8-docstrings==0.2.8
 flake8-future-import==0.4.3
 flake8-mock==0.2
 flake8-pep3101==0.4
-flake8-putty==0.3.2
+flake8-putty==0.4.0
 flake8-string-format==0.2.2
 flake8-tidy-imports==1.0.2
 flake8-tuple==0.2.11