update autoprefixer

Author: chpio

package.json

@@ -25,7 +25,7 @@
   },
   "homepage": "https://github.com/css-modules/browserify-demo",
   "devDependencies": {
-    "autoprefixer": "^5.2.0",
+    "autoprefixer": "^6.0.3",
     "babel-preset-es2015": "^6.0.14",
     "babel-preset-react": "^6.0.14",
     "babelify": "^7.1.0",