Fixing indent issue

On rake assets:precompile was getting an issue:

    ExecJS::RuntimeError: SyntaxError: [stdin]:3:5: unexpected if
  (in /home/gaz/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0/bundler/gems/spree_bootstrap_frontend-2b74b23b9113/app/assets/javascripts/spree/frontend/checkout/payment.js.coffee)

This should fix it.