Disable comparisons feature in uglify compression in production (#2379)

* Disable a micro-option in uglify that appears to be buggy

See #2376

* wrong plugin

* Add a comment

Author: davidascher

packages/react-scripts/config/webpack.config.prod.js

@@ -282,6 +282,11 @@ module.exports = {
     new webpack.optimize.UglifyJsPlugin({
       compress: {
         warnings: false,
+        // Disabled because of an issue with Uglify breaking seemingly valid code:
+        // https://github.com/facebookincubator/create-react-app/issues/2376
+        // Pending further investigation:
+        // https://github.com/mishoo/UglifyJS2/issues/2011
+        comparisons: false,
       },
       output: {
         comments: false,