make 3.x the default branch

Author: xabbuh

composer.json

@@ -36,7 +36,7 @@
         "branch-alias": {
             "1.x-dev": "1.2.x-dev",
             "2.x-dev": "2.2.x-dev",
-            "dev-master": "3.0.x-dev"
+            "3.x-dev": "3.2.x-dev"
         }
     }
 }