update to 1.2.0

Author: lewzylu

src/Qcloud/Cos/Client.php

@@ -12,7 +12,7 @@
 use Qcloud\Cos\TokenListener;
 
 class Client extends GSClient {
-    const VERSION = '1.1.5';
+    const VERSION = '1.2.0';
 
     private $region;       // string: region.
     private $credentials;