Update webpack.prod.conf.js - fix path at comment

Just matching the comment with the actual template file location.

Author: jbruni

template/build/webpack.prod.conf.js

@@ -46,7 +46,7 @@ config.plugins = (config.plugins || []).concat([
   // extract css into its own file
   new ExtractTextPlugin('[name].[contenthash].css'),
   // generate dist index.html with correct asset hash for caching.
-  // you can customize output by editing /build/index.template.html
+  // you can customize output by editing /src/index.html
   // see https://github.com/ampedandwired/html-webpack-plugin
   new HtmlWebpackPlugin({
     filename: '../index.html',