chore(package): update ava to version 0.19.1

https://greenkeeper.io/

Author: greenkeeper[bot]

packages/vuexfire/package.json

@@ -74,7 +74,7 @@
   },
   "homepage": "https://github.com/posva/vuexfire#readme",
   "devDependencies": {
-    "ava": "^0.18.2",
+    "ava": "^0.19.1",
     "babel-preset-es2015": "^6.24.0",
     "babel-preset-stage-2": "^6.22.0",
     "codecov": "^2.1.0",