Make the line shorter and span over 2 lines

qutebrowser/app.py

@@ -130,7 +130,8 @@ def run(args):
 
     if server is None:
         if args.backend is not None:
-            log.init.warning("Changing the backend will not work, the backend from the previous instance will be used!")
+            log.init.warning("Backend from the running" 
+                             "instance will be used")
         sys.exit(usertypes.Exit.ok)
     else:
         server.got_args.connect(lambda args, target_arg, cwd: