set node and npm versions for heroku

Author: lstoll

package.json

@@ -9,4 +9,8 @@
       , "nib": "0.2.0"
       , "socket.io": "0.9.1-1"
     }
+  , "engines": {
+    "node": "0.6.12",
+    "npm": "1.1.4"
+  }
 }