Reformatted piggyback_stripe.js.erb to fix publishable key not being set on page load.

I ran into an issue with the rendered piggyback_stripe.js in my markup being completely empty (I'm assuming stripe_method value wasn't being set). Reformatting the code in that file fixed the issue for me, although I have no idea exactly what was causing the problem.

I can easily replicate the issue by switching between gem versions (official and my fork).