Update eslint-plugin-node requirement from ^5.2.1 to ^6.0.1

Updates the requirements on [eslint-plugin-node](https://github.com/mysticatea/eslint-plugin-node) to permit the latest version.
- [Release notes](https://github.com/mysticatea/eslint-plugin-node/releases)
- [Commits](mysticatea/eslint-plugin-node@v5.2.1...v6.0.1)

package.json

@@ -25,7 +25,7 @@
     "eslint": "^4.15.0",
     "eslint-config-standard": "^11.0.0-beta.0",
     "eslint-plugin-import": "^2.8.0",
-    "eslint-plugin-node": "^5.2.1",
+    "eslint-plugin-node": "^6.0.1",
     "eslint-plugin-promise": "^4.1.1",
     "eslint-plugin-standard": "^3.0.1",
     "mocha": "^4.1.0",