chore(package): update ava to version 3.8.0

Closes #6

Author: greenkeeper[bot]

package.json

@@ -30,7 +30,7 @@
     "slug": "^0.9.1"
   },
   "devDependencies": {
-    "ava": "^0.23.0",
+    "ava": "^3.8.0",
     "axios": "^0.17.0",
     "eslint": "^4.9.0",
     "eslint-config-standard": "^10.2.1",