fix(build): add react minification support

Fix #2110

Author: filipesilva

packages/angular-cli/models/webpack-build-production.ts

@@ -24,6 +24,9 @@ export const getWebpackProdConfigPartial = function(projectRoot: string, appConf
     },
     plugins: [
       new WebpackMd5Hash(),
+      new webpack.DefinePlugin({
+        'process.env.NODE_ENV': 'production'
+      }),
       new webpack.optimize.UglifyJsPlugin(<any>{
         mangle: { screw_ie8 : true },
         compress: { screw_ie8: true },