[triggers] Add missing brackets

has_focus is a method of the Gtk.Window instance so it's necessary to add
brackets after the method name. Otherwise python returns just the reference
to the method and not the result of the method.

triggers/triggers.py

@@ -115,7 +115,7 @@ class Triggers(GajimPlugin):
         if not ctrl:
             # Does not apply in this case
             return True
-        has_focus = ctrl.parent_win.window.has_focus
+        has_focus = ctrl.parent_win.window.has_focus()
         if has_focus and rule['has_focus'] == 'no':
             return False
         elif not has_focus and rule['has_focus'] == 'yes':