Move to HTTPS

You guys! All of the communication with Gradle servers is done over unencrypted http!

This means that anybody installing gradle on a hostile network has a high risk of installing malicious software via trivial attacks!

This is a big security vulnerability which should be fixed immediately.. shouldn't cost you more than sixty bucks to do it properly.

This patch will _currently_ break gradle, but once you have your SSL certificates installed properly, it'll work just fine.

Please fix and merge ASAP!