Fix for #91 (#92)

URL check to make sure that it starts with 'http'

Author: Zombaya

src/Http/GraphRequest.php

@@ -415,6 +415,11 @@ private function _getDefaultHeaders()
     */
     private function _getRequestUrl()
     {
+        //Send request with opaque URL
+        if (stripos($this->endpoint, "http") === 0) {
+            return $this->endpoint;
+        }
+
         return $this->apiVersion . $this->endpoint;
     }