Add composer.json branch alias for Pico 3.0

composer.json

@@ -31,7 +31,8 @@
     "extra": {
         "installer-name": "default",
         "branch-alias": {
-            "dev-master": "2.1.x-dev"
+            "dev-master": "2.1.x-dev",
+            "dev-pico-3.0": "3.0.x-dev"
         }
     }
 }