fix(package): update autoprefixer to version 9.4.2

Closes #96

Author: greenkeeper[bot]

package.json

@@ -29,7 +29,7 @@
   },
   "homepage": "https://github.com/bensmithett/style",
   "dependencies": {
-    "autoprefixer": "^8.0.0",
+    "autoprefixer": "^9.4.2",
     "css-loader": "^0.28.2",
     "extract-text-webpack-plugin": "^3.0.2",
     "gulp": "^3.9.0",