Use "support" instead of "back"
Use "support" instead of "back"

Reason for Change
=================
* I was confused when I saw this button. I thought it referred to the browser's "back" action.
* I wondered if this was confusing for anyone else, so I opened this PR.

Changes
=======
* Replace `Back Ruby Together` with `Support Ruby Together`.

rubytogether/rubytogether.org,rubytogether/rubytogether.org,rubytogether/rubytogether.org,rubytogether/rubytogether.org