chore(package): update ava to version 2.4.0

Closes #16

Author: greenkeeper[bot]

package.json

@@ -32,7 +32,7 @@
   "homepage": "https://github.com/lukechilds/base64-async",
   "dependencies": {},
   "devDependencies": {
-    "ava": "^0.25.0",
+    "ava": "^2.4.0",
     "cli-table": "^0.3.1",
     "coveralls": "^3.0.0",
     "eslint-config-xo-lukechilds": "^1.0.0",