306 is now unused.

Regarding http://tools.ietf.org/html/rfc7231#section-6.4.6:

> The 306 status code was defined in a previous version of this
> specification, is no longer used, and the code is reserved.

Thanks @jubianchi for the review!

Author: Hywan

Response/Response.php

@@ -217,13 +217,6 @@ class          Response
      */
     const STATUS_USE_PROXY                         = '305 Use Proxy';
 
-    /**
-     * Switch proxy.
-     *
-     * @const string
-     */
-    const STATUS_SWITCHING_PROXY                   = '306 Switching Proxy';
-
     /**
      * Temporary redirect.
      *