Remove trailing slash in error message.
Remove trailing slash in error message.

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