don't leak Server version for assets.gratipay.com

Hey, I've captured the HTTP request while visiting assets.gratipay.com **_The whole HTTP response is as following_**: ``` GET / HTTP/1.1 Host: assets.gratipay.com:443 Accept: */* Accept-Encoding: gzip, deflate, sdch, br Accept-Language: en-US,en;q=0.8 Origin: https://www.youtube.com Referer: https://www.youtube.com/watch?v=0-gIBjd8Hws User-Agent: Mozilla/5.0 (Windows NT 6.3) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/51.0.2704.103 Safari/537.36 X-Chrome-UMA-Enabled: 1 X-Client-blocked: CIq2yQEIpLbJAQjEtskBCPGcygE= HTTP/1.1 404 cache-control: no-cache content-encoding: gzip content-type: text/html; charset=UTF-8 date: Thu, 14 Jul 2016 10:28:14 GMT server: NetDNA-cache/2.2 status: 404 via: 1.1 vegur x-content-type-options: nosniff x-frame-options: SAMEORIGIN x-gratipay-version: 1976 x-xss-protection: 1; mode=block ``` So as you can see that the "server: NetDNA-cache/2.2" is showing the NetDNA-cache server and version! I hope you'll fix it! Note: If you are not going to fix this one, please close this as informative! :) Thanks, Ahsan Tahir