Do not complain on imports from six

Signed-off-by: Michal Čihař <michal@cihar.com>

pylint.rc

@@ -93,7 +93,7 @@ ignore-mixin-members=yes
 # List of module names for which member attributes should not be checked
 # (useful for modules/projects where namespaces are manipulated during runtime
 # and thus extisting member attributes cannot be deduced by static analysis
-ignored-modules=
+ignored-modules=six.moves
 
 # List of classes names for which member attributes should not be checked
 # (useful for classes with attributes dynamically set).