chore(package): update autoprefixer to version 9.7.6

Closes #343

Author: greenkeeper[bot]

package.json

@@ -42,7 +42,7 @@
     ]
   },
   "devDependencies": {
-    "autoprefixer": "^8.0.0",
+    "autoprefixer": "^9.7.6",
     "babel": "^6.5.2",
     "babel-core": "^6.24.0",
     "babel-eslint": "^8.2.2",