🤖 chore(package.json): Add devDependency xo.

These changes were automatically generated by a transform whose code can be found at:
  - https://github.com/make-github-pseudonymous-again/rejuvenate/blob/1b5252aec880aa76850f97b16980a6ce00c782c4/src/transforms/deps:add-xo.js
Please contact the author of the transform if you believe there was an error.

Author: a-flying-potato

package.json

@@ -64,7 +64,8 @@
     "esdoc-standard-plugin": "1.0.0",
     "fixpack": "4.0.0",
     "np": "7.4.0",
-    "power-assert": "1.6.1"
+    "power-assert": "1.6.1",
+    "xo": "0.42.0"
   },
   "ava": {
     "files": [