Merge pull request #960 from adamtheturtle/pyup-update-yapf-0.25.0-to-0.26.0

Update yapf to 0.26.0

Author: adamtheturtle

dev-requirements.txt

@@ -27,4 +27,4 @@ twine==1.12.1
 versioneer==0.18
 vulture==1.0
 VWS-Python-Mock==2018.12.1.0
-yapf==0.25.0  # Automatic formatting for Python
+yapf==0.26.0  # Automatic formatting for Python