fix: package.json to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-JS-TMP-11501554

Author: snyk-bot

package.json

@@ -35,7 +35,7 @@
     "@types/node": "^12.x",
     "chai": "^4.x",
     "dtslint": "^3.x",
-    "eslint": "^6.x",
+    "eslint": "^9.0.0",
     "eslint-config-google": "^0.14.x",
     "mocha": "^7.x",
     "node-mocks-http": "roshangade/node-mocks-http",