Update ava to the latest version 🚀 (#112)

* chore(package): update ava to version 0.18.0

https://greenkeeper.io/

* chore: update ava to version 0.19.1

Author: greenkeeper[bot]

packages/stylelint-config-wordpress/package.json

@@ -36,7 +36,7 @@
     "node": ">=6.9.1"
   },
   "devDependencies": {
-    "ava": "^0.17.0",
+    "ava": "^0.19.1",
     "eslint": "^3.0.0",
     "eslint-config-stylelint": "^6.0.0",
     "eslint-plugin-ava": "^4.0.0",