Fixes issue with $parameters of type array is incompatible with the t…

…ype string expected by parameter $query of apiRequest().

src/Fastspring/ApiClient.php

@@ -89,7 +89,7 @@ public function __construct($username = null, $password = null)
      *
      * @param string $method         Method of HTTP request like PUT, GET, POST
      * @param string $path           Path of API
-     * @param string $query          Query parameters
+     * @param array  $query          Query parameters array
      * @param string $formParameters Form parameters
      * @param string $jsonPayload    Json payload
      *