chore(package): update ava to version 3.7.1

Closes #33

Author: greenkeeper[bot]

package.json

@@ -8,7 +8,7 @@
   },
   "dependencies": {},
   "devDependencies": {
-    "ava": "^0.25.0",
+    "ava": "^3.7.1",
     "fixpack": "^2.3.1",
     "prettier": "^1.13.5",
     "standard": "^11.0.0"