fix: package.json to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/npm:deep-extend:20180409

package.json

@@ -42,7 +42,7 @@
     "chalk": "^2.0.0",
     "lodash": "~4.17.3",
     "meow": "^5.0.0",
-    "update-notifier": "^2.0.0"
+    "update-notifier": "^2.5.0"
   },
   "devDependencies": {
     "chai": "4.1.2",