Update package.json: engine npm 2.4.x

package.json

@@ -15,7 +15,7 @@
   },
   "engines": {
     "node": "0.10.x",
-    "npm": "1.3.x"
+    "npm": "2.4.x"
   },
   "dependencies": {
     "async": "~0.9.0",