Revert "empirically if we want sourcemaps which work for dev we need eval-source-map"

This change causes Node to crash during builds in some configurations.  It also
grows the production bundle size to ~4x what it was before.

This reverts commit 9f4ce2dcf2.

webpack.config.js

@@ -175,7 +175,7 @@ module.exports = {
             chunks: ['mobileguide'],
         }),
     ],
-    devtool: 'eval-source-map',
+    devtool: 'source-map',
 
     // configuration for the webpack-dev-server
     devServer: {