feat(build): Add source maps to production

We don't have the same precautions as other sites as our code base is
open source, so we might as well make it easier on us to debug
production errors

webpack.frame-runner.js

@@ -1,11 +1,12 @@
 const webpack = require('webpack');
 const path = require('path');
+const UglifyPlugin = require('uglifyjs-webpack-plugin');
 
 const __DEV__ = process.env.NODE_ENV !== 'production';
 
 module.exports = {
   entry: './client/frame-runner.js',
-  devtool: __DEV__ ? 'inline-source-map' : null,
+  devtool: __DEV__ ? 'inline-source-map' : 'source-map',
   node: {
     // Mock Node.js modules that Babel require()s but that we don't
     // particularly care about.
@@ -68,4 +69,12 @@ if (__DEV__) {
     // prevents build on error
     new webpack.NoEmitOnErrorsPlugin()
   );
+} else {
+  module.exports.plugins.push(
+    new UglifyPlugin({
+      test: /\.js($|\?)/i,
+      cache: true,
+      sourceMap: true
+    })
+  );
 }