Allow to use postcss for CSS @imports. (#564)

Based on facebook/create-react-app#929

Author: arunoda

dist/server/build.js

@@ -22,7 +22,7 @@ module.exports = function (storybookBaseConfig) {
   newConfig.module.loaders = [].concat((0, _toConsumableArray3.default)(storybookBaseConfig.module.loaders), [{
     test: /\.css?$/,
     include: _utils.includePaths,
-    loaders: [require.resolve('style-loader'), require.resolve('css-loader'), require.resolve('postcss-loader')]
+    loaders: [require.resolve('style-loader'), require.resolve('css-loader') + '?importLoaders=1', require.resolve('postcss-loader')]
   }, {
     test: /\.json$/,
     include: _utils.includePaths,

dist/server/config/defaults/webpack.config.js

@@ -11,7 +11,7 @@ module.exports = (storybookBaseConfig) => {
       include: includePaths,
       loaders: [
         require.resolve('style-loader'),
-        require.resolve('css-loader'),
+        `${require.resolve('css-loader')}?importLoaders=1`,
         require.resolve('postcss-loader'),
       ],
     },