extract-text-webpack-plugin@>=2 api changed (#632)

Author: helloyou2012

docs/en/configurations/extract-css.md

@@ -22,8 +22,8 @@ module.exports = {
         options: {
           loaders: {
             css: ExtractTextPlugin.extract({
-              loader: 'css-loader',
-              fallbackLoader: 'vue-style-loader' // <- this is a dep of vue-loader, so no need to explicitly install if using npm3
+              use: 'css-loader',
+              fallback: 'vue-style-loader' // <- this is a dep of vue-loader, so no need to explicitly install if using npm3
             })
           }
         }