chore(package): update ava to version 0.18.1

https://greenkeeper.io/

Author: greenkeeper[bot]

package.json

@@ -28,7 +28,7 @@
   },
   "devDependencies": {
     "aureooms-js-itertools": "^3.1.0",
-    "ava": "^0.17.0",
+    "ava": "^0.18.1",
     "babel-cli": "^6.18.0",
     "babel-polyfill": "^6.16.0",
     "babel-preset-latest": "^6.16.0",