Update composer.json branch aliases

composer.json

@@ -51,8 +51,7 @@
     },
     "extra": {
         "branch-alias": {
-            "dev-master": "2.0.x-dev",
-            "dev-pico-2.1": "2.1.x-dev"
+            "dev-master": "2.1.x-dev"
         }
     }
 }