fix(package): update gulp-autoprefixer to version 5.0.0

Author: greenkeeper[bot]

package.json

@@ -24,7 +24,7 @@
   "dependencies": {
     "foundation-sites": "^6.3.1",
     "gulp": "^3.9.0",
-    "gulp-autoprefixer": "^4.0.0",
+    "gulp-autoprefixer": "^5.0.0",
     "gulp-concat": "^2.6.1",
     "gulp-load-plugins": "^1.1.0",
     "gulp-pug": "^3.3.0",