fix(package): update ava to version 3.5.1

Closes #176

Author: greenkeeper[bot]

package.json

@@ -21,7 +21,7 @@
   },
   "homepage": "https://github.com/superawesomelabs/leo#readme",
   "dependencies": {
-    "ava": "^0.17.0",
+    "ava": "^3.5.1",
     "babel-cli": "^6.18.0",
     "babel-core": "^6.18.0",
     "babel-eslint": "^7.0.0",