devkit: install r.js

external/amber-dev/package.json

@@ -17,6 +17,7 @@
   "dependencies": {
     "amd-config-builder": "^0.2.0",
     "amdefine": ">=0.1.1",
-    "es6-promise": "^2.0.0"
+    "es6-promise": "^2.0.0",
+    "requirejs": "^2.1.19"
   }
 }