Add sourcemap option to postCSS-loader options (vuejs-templates#1039)

* Add sourcemap option to postCSS-loader options

* Update utils.js

* fix condition, should als fail on `undefined`

Author: LinusBorg

template/build/utils.js

@@ -23,12 +23,15 @@ exports.cssLoaders = function (options) {
   }
 
   var postcssLoader = {
-    loader: 'postcss-loader'
+    loader: 'postcss-loader',
+    options: {
+      sourceMap: options.sourceMap
+    }
   }
 
   // generate loader string to be used with extract text plugin
   function generateLoaders (loader, loaderOptions) {
-    const loaders = options.usePostCSS !== false ? [cssLoader, postcssLoader] : [cssLoader]
+    const loaders = options.usePostCSS ? [cssLoader, postcssLoader] : [cssLoader]
     if (loader) {
       loaders.push({
         loader: loader + '-loader',