Update ava to the latest version 🚀 (#434)

* chore(package): update ava to version 0.19.0

https://greenkeeper.io/

* yarn.lock

Author: greenkeeper[bot]

package.json

@@ -19,7 +19,7 @@
     "webpack": "2"
   },
   "devDependencies": {
-    "ava": "^0.18.0",
+    "ava": "^0.19.0",
     "babel-cli": "^6.18.0",
     "babel-core": "^6.0.0",
     "babel-eslint": "^7.1.0",