Added meta tag for referrer, so that only the origin is sent to third party...

Added meta tag for referrer, so that only the origin is sent to third party sites, instead of the entire URL, thus avoiding the leak of sensitive information like password reset tokens.

app/views/layouts/_head.html.haml

@@ -3,6 +3,7 @@
   %meta{charset: "utf-8"}
   %meta{'http-equiv' => 'X-UA-Compatible', content: 'IE=edge'}
   %meta{content: "GitLab Community Edition", name: "description"}
+  %meta{name: 'referrer', content: 'origin'}
   %title= page_title