Include es6-shim in the build process

package.json

@@ -7,6 +7,7 @@
     "build": "mkdir -p build; browserify src/index.js -o build/app.js"
   },
   "devDependencies": {
+    "es6-shim": "^0.35.1",
     "ethereumjs-block": "^1.2.2",
     "ethereumjs-vm": "^1.3.0",
     "merkle-patricia-tree": "^2.1.2",

src/index.js

+require('es6-shim');
 var app = require("./app.js");
 var $ = require("jquery");