chore(deps): update linters (#213)

Author: Renovate Bot

packages/google-cloud-oslogin/package.json

@@ -45,8 +45,8 @@
   },
   "devDependencies": {
     "codecov": "^3.0.0",
-    "eslint": "^5.0.0",
-    "eslint-config-prettier": "^4.0.0",
+    "eslint": "^6.0.0",
+    "eslint-config-prettier": "^6.0.0",
     "eslint-plugin-node": "^9.0.0",
     "eslint-plugin-prettier": "^3.0.0",
     "jsdoc-baseline": "^0.1.0",