cssnano: safe by default, allow config in vue.config.js

Author: yyx990803

lib/style-rewriter.js

@@ -1,6 +1,7 @@
 var postcss = require('postcss')
 var selectorParser = require('postcss-selector-parser')
 var cache = require('lru-cache')(100)
+var assign = require('object-assign')
 var options = require('./compilers/options')
 
 var currentId
@@ -58,9 +59,10 @@ module.exports = function (id, css, scoped) {
     }
     // minification
     if (process.env.NODE_ENV === 'production') {
-      plugins.push(require('cssnano')({
-        autoprefixer: false
-      }))
+      plugins.push(require('cssnano')(assign({
+        autoprefixer: false,
+        safe: true
+      }, options.cssnano)))
     }
     currentId = id
     return postcss(plugins)