chore(package): update ava to version 2.4.0

Closes #28

Author: greenkeeper[bot]

package.json

@@ -42,7 +42,7 @@
     "pify": "^3.0.0"
   },
   "devDependencies": {
-    "ava": "^0.25.0",
+    "ava": "^2.4.0",
     "coveralls": "^3.0.0",
     "eslint-config-xo-lukechilds": "^1.0.0",
     "got": "^8.0.0",