twitter-server: Remove .json extension from /admin/toggles

Problem

The admin endpoint for Toggles currently ends with ".json". Once
mutations are allowed via POST/PUT/DELETE this extenstion will look
out of place.

As an example, this would not be a great path:
`DELETE /admin/toggles.json/com.twitter.somelib/com.twitter.somelib.Toggle`

Solution

Remove the ".json" extension such that the admin endpoint is available
at "/admin/toggles".

RB_ID=849646

CHANGES

@@ -19,6 +19,10 @@ New Features
    * Add optional HTTP request parameter `filter` to `/admin/registry.json`
      allowing for simple filtering of the returned JSON. ``RB_ID=842784``
 
+   * Add admin endpoint, `/admin/toggles`, for
+     `c.t.finagle.toggle.StandardToggleMap` registered `Toggles`.
+     ``RB_ID=847434``
+
 Breaking API Changes
 ~~~~~~~~~~~~~~~~~~~~
 

src/main/scala/com/twitter/server/Admin.scala

@@ -116,7 +116,7 @@ trait Admin { self: App with AdminHttpServer with Stats =>
         path = "/admin/registry.json", handler = new RegistryHandler,
         alias = "Registry", group = Some(Grouping.ProcessInfo), includeInIndex = true),
       Route(
-        path = "/admin/toggles.json", handler = new ToggleHandler(),
+        path = "/admin/toggles", handler = new ToggleHandler(),
         alias = "Toggles", group = Some(Grouping.ProcessInfo), includeInIndex = true),
       Route(
         path = "/favicon.ico", ResourceHandler.fromJar(