chore(package): update ava to version 0.21.0 (#6)

Author: greenkeeper[bot]

package.json

@@ -44,7 +44,7 @@
   },
   "homepage": "https://github.com/lukechilds/create-node#readme",
   "devDependencies": {
-    "ava": "^0.19.1",
+    "ava": "^0.21.0",
     "babel-cli": "^6.9.0",
     "babel-plugin-add-module-exports": "^0.2.1",
     "babel-preset-es2015": "^6.9.0",