Minify and map css (facebook#2013)

Minify and map css

Author: viankakrisna

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

@@ -197,6 +197,8 @@ module.exports = {
                   loader: 'css-loader',
                   options: {
                     importLoaders: 1,
+                    minimize: true,
+                    sourceMap: true,
                   },
                 },
                 {