chore(package): update ava to version 2.4.0

Closes #55

Author: greenkeeper[bot]

package.json

@@ -12,7 +12,7 @@
   },
   "repository": "rohmanhm/nullfined",
   "devDependencies": {
-    "ava": "^1.2.1",
+    "ava": "^2.4.0",
     "lodash.camelcase": "^4.3.0",
     "rollup": "^1.2.3",
     "rollup-plugin-babel": "^4.3.2",