Update dependency xo to ^0.56.0

Author: renovate[bot]

package.json

@@ -97,7 +97,7 @@
     "nyc": "15.1.0",
     "power-assert": "1.6.1",
     "regenerator-runtime": "0.13.7",
-    "xo": "^0.33.1"
+    "xo": "^0.56.0"
   },
   "files": [
     "lib"