Fix referals for :back and relative URL installs.

CHANGELOG

@@ -2,6 +2,7 @@ Please view this file on the master branch, on stable branches it's out of date.
 v 8.0.4
   - Fix Message-ID header to be RFC 2111-compliant to prevent e-mails being dropped (Stan Hu)
+  - Fix referrals for :back and relative URL installs
 v 8.0.3
   - Fix URL shown in Slack notifications

app/views/layouts/_head.html.haml

@@ -3,7 +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'}
+  %meta{name: 'referrer', content: 'origin-when-cross-origin'}
   %title= page_title