Fixed branch alias

Author: GrahamCampbell

composer.json

@@ -50,7 +50,7 @@
     "extra": {
         "branch-alias": {
             "dev-2.x": "2.19.x-dev",
-            "dev-master": "3.0.x-dev"
+            "dev-master": "3.1.x-dev"
         }
     }
 }