Amazon composer version adjustment due to packagist error.

composer.json

@@ -8,6 +8,12 @@
         }
     ],
     "license": "GPL-2.0",
+    "repositories": [
+        {
+            "type": "vcs",
+            "url": "https://github.com/zendframework/zendservice_amazon"
+        }
+    ],
     "require": {
         "aferrandini/phpqrcode": "1.0.1",
         "jasig/phpcas": "1.3.3",