Bell activity is not styled

[lunks]

I'm not sure if this should be reported here or on powerline it self, but bell activity does not apply the style correctly. You can reproduce by running:

sleep 1 && tput bel

Then, move away from the window.

[lunks]

Solved by adding:

set-option -g window-status-bell-style none

[xx4h]

Also see #342 (comment)