offlineimap/ files singleton-comparison

This patch change these errors in the offlineimap folder

C0121: Comparison to None should be 'expr is None' (singleton-comparison)
C0121: Comparison to None should be 'expr is not None' (singleton-comparison)

offlineimap/init.py

@@ -245,7 +245,7 @@ class OfflineImap():
 
         # Which ui to use? CLI option overrides config file.
         ui_type = config.getdefault('general', 'ui', 'ttyui')
-        if options.interface != None:
+        if options.interface is not None:
             ui_type = options.interface
         if '.' in ui_type:
             # Transform Curses.Blinkenlights -> Blinkenlights.