Adds rel="noopener noreferrer" to _blank links inside comments

For more details, check out https://mathiasbynens.github.io/rel-noopener/ for instance

Signed-off-by: Thomas Citharel <tcit@tcit.fr>

core/js/public/comments.js

@@ -43,7 +43,7 @@
 				}
 
 				var linkText = url.replace(self.protocolRegex, '');
-				return '<a class="external" target="_blank" href="' + url + '">' + linkText + '</a>';
+				return '<a class="external" target="_blank" rel="noopener noreferrer" href="' + url + '">' + linkText + '</a>';
 			});
 		},