chore(package): update ava to version 0.19.0 (#21)

Author: greenkeeper[bot]

package.json

@@ -15,7 +15,7 @@
     "sugarss": "^0.2.0"
   },
   "devDependencies": {
-    "ava": "^0.18.1",
+    "ava": "^0.19.0",
     "coveralls": "^2.11.12",
     "nyc": "^10.0.0",
     "rewire": "^2.5.2",