Feature/week7 mod1

I ran into two problem
1. in `spec/features/invite_friend_spec.rb:41`, if not add `sleep(2)`, the test will failed.
    in `environments/test.rb:17`, if use `localhost:52662`, the test will also failed.
2. in `payments.js`, disable submit is not working, it also send twice submit, then raise an exception from stripe.
If you use the `form_tag` form builder, things like the `for` attribute will be taken care of for you.