use latest versions of node and npm on heroku

Author: zeke

package.json

@@ -9,6 +9,10 @@
   "dependencies": {
     "express": "~3.3.4"
   },
+  "engines": {
+    "node": "0.10.13",
+    "npm": "1.3.2"
+  },
   "repository": {
     "type": "git",
     "url": "https://github.com/heroku/node-js-sample"