chore(package): update ava to version 1.4.0

Closes #67

Author: greenkeeper[bot]

package.json

@@ -48,7 +48,7 @@
     "url": "^0.11.0"
   },
   "devDependencies": {
-    "ava": "^0.20.0",
+    "ava": "^1.4.0",
     "babel-cli": "^6.16.0",
     "babel-core": "^6.25.0",
     "babel-eslint": "^7.2.3",