Update dependency xo to v0.28.1

Author: renovate-bot

package.json

@@ -48,7 +48,7 @@
     "esdoc-standard-plugin": "1.0.0",
     "np": "5.2.1",
     "nyc": "14.1.1",
-    "xo": "0.26.1"
+    "xo": "0.28.1"
   },
   "files": [
     "lib"