Make GZIP permanent

In April (before gzip), Data Transfer was 46% of the AWS bill (excluding reserved instances).

In May (after gzip) it has gone down to 37% of the bill which represents a monthly saving of about $900.

Every bit helps

cc @tackley @cantlin 

:dollar: 

![jansen](https://cloud.githubusercontent.com/assets/76709/3090313/ab2f1f60-e58a-11e3-8fe2-790625c9bae9.gif)