sign up button is not working of student ambassadors page bug 893329

https://bugzilla.mozilla.org/show_bug.cgi?id=893329

Looks like this bug is a result of commit: https://github.com/mozilla/bedrock/commit/b6eed50f1f0757757721cd953b2a136194d111b2#media/js/base/footer-email-form.js

Simplest fix was to change the id of the ambassadors page form, since (I'm assuming) it was originally taken from the contribute page template, and hence had the same id.