docs(README): replace postcss-cssnext with postcss-preset-env (webpack#379)

Author: halfzebra

README.md

@@ -39,7 +39,7 @@ module.exports = {
   parser: 'sugarss',
   plugins: {
     'postcss-import': {},
-    'postcss-cssnext': {},
+    'postcss-preset-env': {},
     'cssnano': {}
   }
 }
@@ -179,8 +179,7 @@ module.exports = ({ file, options, env }) => ({
   parser: file.extname === '.sss' ? 'sugarss' : false,
   plugins: {
     'postcss-import': { root: file.dirname },
-    'postcss-cssnext': options.cssnext ? options.cssnext : false,
-    'autoprefixer': env === 'production' ? options.autoprefixer : false,
+    'postcss-preset-env': options.presetEnv ? options.presetEnv : false,
     'cssnano': env === 'production' ? options.cssnano : false
   }
 })
@@ -212,7 +211,7 @@ module.exports = ({ file, options, env }) => ({
     ident: 'postcss',
     plugins: (loader) => [
       require('postcss-import')({ root: loader.resourcePath }),
-      require('postcss-cssnext')(),
+      require('postcss-preset-env')(),
       require('autoprefixer')(),
       require('cssnano')()
     ]