Drop using XO for now until a new version is out that uses ESLint 5

sindresorhus · sindresorhus · commit b4bb64aacb9d · 2018-06-24T13:59:50.000+07:00
Some weird dependency problem...
diff --git a/package.json b/package.json
@@ -40,7 +40,7 @@
 		"node": ">=4"
 	},
 	"scripts": {
-		"test": "xo && nyc ava",
+		"test": "nyc ava",
 		"coveralls": "nyc report --reporter=text-lcov | coveralls"
 	},
 	"files": [
