Configure webpack to stop on error

When building the project, we want webpack to die with an exit code
other than 0.  Otherwise, we risk masking and silently ignoring errors.

Change-Id: Ic501effd3e9b21c785c09fc1ca189c8444b05f3c
Closes-bug: 1654051

package.json

@@ -67,7 +67,7 @@
     "es6-promise": "~3.2.1"
   },
   "scripts": {
-    "build": "webpack",
+    "build": "webpack --bail",
     "lint": "eslint --max-warnings 0 src",
     "start": "webpack-dev-server --progress",
     "test": "karma start --single-run",

webpack.config.js

@@ -3,6 +3,7 @@ require('es6-promise').polyfill(); // https://github.com/webpack/css-loader/issu
 module.exports = {
   devtool: 'inline-source-map',
   entry: __dirname + '/src/js/index.js',
+  bail: true,
   output: {
     path: __dirname + '/dist',
     publicPath: '/',