Update xo

Author: wooorm

package.json

@@ -52,7 +52,7 @@
     "tape": "^5.0.0",
     "type-coverage": "^2.0.0",
     "typescript": "^4.0.0",
-    "xo": "^0.39.0"
+    "xo": "^0.42.0"
   },
   "scripts": {
     "build": "rimraf \"{index,test}.d.ts\" && tsc && type-coverage",