chore(package): update xo to version 0.20.1 (#13)

Closes #12

Author: lukechilds

package.json

@@ -52,6 +52,6 @@
     "eslint-config-xo-lukechilds": "^1.0.0",
     "nyc": "^11.0.2",
     "window": "^4.1.0",
-    "xo": "^0.18.2"
+    "xo": "^0.20.1"
   }
 }