chore(package): update ava to version 3.7.1

Closes #40

Author: greenkeeper[bot]

package.json

@@ -41,7 +41,7 @@
     "shelljs": "^0.8.3"
   },
   "devDependencies": {
-    "ava": "^2.0.0",
+    "ava": "^3.7.1",
     "coveralls": "^3.0.2",
     "eslint": "^5.14.0",
     "eslint-config-prettier": "^6.1.0",