added 'flagged_by' i18n.

app/assets/javascripts/admin/templates/flags.js.handlebars

@@ -13,7 +13,7 @@
     <tr>
       <th class='user'></th>
       <th class='excerpt'></th>
-      <th class='flaggers'>Flagged by</th>
+      <th class='flaggers'>{{i18n admin.flags.flagged_by}}</th>
       <th class='last-flagged'></th>
       <th class='action'></th>
     </tr>

config/locales/client.en.yml

@@ -597,6 +597,7 @@ en:
         clear_title: "dismiss all flags on this post (will unhide hidden posts)"
         delete: "Delete Post"
         delete_title: "delete post (if its the first post delete topic)"
+        flagged_by: "Flagged by"
 
       customize: 
         title: "Customize"