Fixed constructor to correctly cache when an auth token is passed (JorgenPhi#32)

Author: dstelljes

src/snapchat.php

@@ -73,6 +73,7 @@ public function __construct($username = NULL, $password = NULL, $auth_token = NU
     }
     elseif (!empty($auth_token)) {
       $this->auth_token = $auth_token;
+      $this->cache = new SnapchatCache();
       $this->username = $username;
     }
   }