Add type cast to stop IE8 erroring in admin.
Add type cast to stop IE8 erroring in admin.

IE was not treating the reponse of `data` as a string and as such it
didn't have a `indexOf` method. Using type coercion to force a string
fixes this.

ggoral/whitehall,alphagov/whitehall,askl56/whitehall,ggoral/whitehall,YOTOV-LIMITED/whitehall,alphagov/whitehall,alphagov/whitehall,ggoral/whitehall,robinwhittleton/whitehall,alphagov/whitehall,YOTOV-LIMITED/whitehall,robinwhittleton/whitehall,askl56/whitehall,ggoral/whitehall,askl56/whitehall,hotvulcan/whitehall,hotvulcan/whitehall,YOTOV-LIMITED/whitehall,robinwhittleton/whitehall,YOTOV-LIMITED/whitehall,robinwhittleton/whitehall,askl56/whitehall,hotvulcan/whitehall,hotvulcan/whitehall