fixing for bad 3.1.0 version

Author: Nil Portugués Calderó

composer.json

@@ -14,7 +14,7 @@
     ],
     "require": {
         "php": ">=5.5.0",
-        "nilportugues/api-transformer": "^3.0.0",
+        "nilportugues/api-transformer": "<=3.0.0",
         "symfony/psr-http-message-bridge" : "^0.2|^0.3"
     },
     "require-dev": {