fix(throttle): change throttle to throw exception instead of retry

Author: shawnhind

lib/CurlRequest.php

@@ -152,7 +152,7 @@ protected static function processRequest($ch, $url)
             },
 
             function () {
-                usleep(250000);
+                throw new Exception\ThrottleException("Could not get lock on API resource in Redis.");
             });
 
             if (isset($output)) {

lib/Exception/ThrottleException.php

@@ -0,0 +1,7 @@
+<?php
+
+namespace PHPShopify\Exception;
+
+class ThrottleException extends \Exception
+{
+}