chore(package): update ava to version 2.2.0

Closes #27

Author: greenkeeper[bot]

package.json

@@ -16,7 +16,7 @@
     "raj": "1.0.0"
   },
   "devDependencies": {
-    "ava": "^0.25.0",
+    "ava": "^2.2.0",
     "babel-cli": "^6.24.1",
     "babel-core": "^6.25.0",
     "babel-preset-es2015": "^6.24.1",