Don't attempt to set Referrer policy in Safari

While Safari supports the policy, it does not (currently, as of 9.x)
recognize `origin-when-cross-origin` as a valid value, so we omit the
policy entirely under Safari.

Closes #5609

CHANGELOG

@@ -12,6 +12,7 @@ v 8.4.0 (unreleased)
   - Add link to merge request on build detail page
   - Revert back upvote and downvote button to the issue and MR pages
   - Swap position of Assignee and Author selector on Issuables (Zeger-Jan van de Weg)
+  - Fix version check image in Safari
 
 v 8.3.3 (unreleased)
   - Fix project transfer e-mail sending incorrect paths in e-mail notification (Stan Hu)

app/views/layouts/_head.html.haml

 %head{prefix: "og: http://ogp.me/ns#"}
   %meta{charset: "utf-8"}
   %meta{'http-equiv' => 'X-UA-Compatible', content: 'IE=edge'}
-  %meta{name: 'referrer', content: 'origin-when-cross-origin'}
-
-  %meta{name: "description", content: page_description}
 
   -# Open Graph - http://ogp.me/
   %meta{property: 'og:type',        content: "object"}
@@ -20,8 +17,8 @@
   %meta{property: 'twitter:image',        content: page_image}
   = page_card_meta_tags
 
-  - page_title "GitLab"
-  %title= page_title
+  %title= page_title('GitLab')
+  %meta{name: "description", content: page_description}
 
   = favicon_link_tag 'favicon.ico'
 
@@ -34,6 +31,8 @@
 
   = include_gon
 
+  - unless browser.safari?
+    %meta{name: 'referrer', content: 'origin-when-cross-origin'}
   %meta{name: 'viewport', content: 'width=device-width, initial-scale=1, maximum-scale=1'}
   %meta{name: 'theme-color', content: '#474D57'}