Include sourcemaps in the default options

Author: Patrick Taddey

lib/loaders/css-extract.js

@@ -24,7 +24,9 @@ module.exports = {
     prependLoaders(webpackConfig, loaders) {
         if (!webpackConfig.extractCss) {
 
-            const options = {};
+            const options = {
+                sourceMap: webpackConfig.useSourceMaps,
+            };
 
             // If the CSS extraction is disabled, use the
             // style-loader instead.