chore(package): update xo to version 0.20.2

Closes #11

Author: greenkeeper[bot]

package.json

@@ -40,6 +40,6 @@
     "nyc": "^11.0.2",
     "pem": "^1.9.7",
     "pify": "^3.0.0",
-    "xo": "^0.19.0"
+    "xo": "^0.20.2"
   }
 }