Add a Pinned Tab icon for Safari

See http://apple.co/1SCRzrw

Closes #13540

[ci skip]

app/views/layouts/_head.html.haml

@@ -44,6 +44,7 @@
   = favicon_link_tag 'touch-icon-ipad.png',          rel: 'apple-touch-icon', sizes: '76x76'
   = favicon_link_tag 'touch-icon-iphone-retina.png', rel: 'apple-touch-icon', sizes: '120x120'
   = favicon_link_tag 'touch-icon-ipad-retina.png',   rel: 'apple-touch-icon', sizes: '152x152'
+  %link{rel: 'mask-icon', href: image_path('logo.svg'), color: 'rgb(226, 67, 41)'}
 
   -# Windows 8 pinned site tile
   %meta{name: 'msapplication-TileImage', content: image_path('msapplication-tile.png')}