[FIX] import error

Error:
  class MailChatController(openerp.addons.bus.controllers.main.BusController):
  AttributeError: 'module' object has no attribute 'bus'

mail_base/README.rst

@@ -25,4 +25,4 @@ Usage instructions: `<doc/index.rst>`_
 
 Changelog: `<doc/changelog.rst>`_
 
-Tested on Odoo 9.0 c8cd67c5d98b410cabe0a6efb3347a8a4de731d8
+Tested on Odoo 9.0 ed463864366029f8d4289db831fcdc196fc716cb

mail_base/controllers/main.py

@@ -1,9 +1,9 @@
 # -*- coding: utf-8 -*-
 from openerp.http import request
-import openerp
+from openerp.addons.bus.controllers.main import BusController
 
 
-class MailChatController(openerp.addons.bus.controllers.main.BusController):
+class MailChatController(BusController):
     # -----------------------------
     # Extends BUS Controller Poll
     # -----------------------------