chore(package): update autoprefixer to version 7.1.2

Closes #2353

package.json

@@ -157,7 +157,7 @@
     "webpack-isomorphic-tools": "2.6.6"
   },
   "devDependencies": {
-    "autoprefixer": "^6.7.7",
+    "autoprefixer": "^7.1.2",
     "babel-core": "^6.24.1",
     "babel-eslint": "^7.2.3",
     "babel-gettext-extractor": "git+https://github.com/muffinresearch/babel-gettext-extractor.git#0d39d3882bc846e7dcb6c9ff6463896c96920ce6",