chore(package): update xo to version 0.28.3

Closes #56

Author: greenkeeper[bot]

package.json

@@ -36,7 +36,7 @@
     "husky": "^3.0.0",
     "semantic-release": "^15.0.0",
     "validate-commit-msg": "^2.12.2",
-    "xo": "^0.18.2"
+    "xo": "^0.28.3"
   },
   "xo": {
     "space": 4,