replace all instances of "ends_with?" with "end_with?" (#15745)

The "ends_with?" method is just a Rails alias of Ruby's "end_with?" method.
Using the latter makes the code less brittle.

app/controllers/media_proxy_controller.rb

@@ -37,7 +37,7 @@ class MediaProxyController < ApplicationController
   end
 
   def version
-    if request.path.ends_with?('/small')
+    if request.path.end_with?('/small')
       :small
     else
       :original