Enforcing six version on setup.py

This plugin uses a function from six that was introduced on version 1.12, so now we will install the right six version.

Author: thiagoalmeidasa

setup.py

@@ -73,7 +73,7 @@
     packages=[__plugin_name__.lower()],
     package_data = __pkg_data__,
     install_requires=[
-        'six',
+        'six>=1.12',
     ],
 
     entry_points="""