chore(deps): update dependency ava to v6

Author: renovate[bot]

package.json

@@ -11,7 +11,7 @@
   },
   "license": "MIT",
   "devDependencies": {
-    "ava": "^0.25.0",
+    "ava": "^6.0.0",
     "babel-cli": "^6.26.0",
     "babel-eslint": "^8.2.3",
     "babel-plugin-istanbul": "^4.1.6",