chore(package): update xo to version 0.28.0

Closes #5

Author: greenkeeper[bot]

package.json

@@ -30,7 +30,7 @@
     "husky": "^1.2.0",
     "nyc": "^13.1.0",
     "standard-version": "^5.0.0",
-    "xo": "^0.23.0"
+    "xo": "^0.28.0"
   },
   "xo": {
     "semicolon": false,