add build script to package file

@@ -11,5 +11,8 @@
   "repository" : {
   "repository" : {
     "type" : "git",
     "type" : "git",
     "url" : "https://github.com/mikeric/rivets.git"
     "url" : "https://github.com/mikeric/rivets.git"
+  },
+  "scripts" : {
+    "build" : "coffee -o lib -c src"
   }
   }
 }
 }