chore(package): update xo to version 0.23.0

Closes #12

Author: greenkeeper[bot]

package.json

@@ -40,6 +40,6 @@
     "nyc": "^11.0.2",
     "pretty-bytes": "^5.0.0",
     "time-span": "^2.0.0",
-    "xo": "^0.19.0"
+    "xo": "^0.23.0"
   }
 }