chore(deps): update linters (#189)

Author: Renovate Bot

packages/google-cloud-kms/package.json

@@ -43,8 +43,8 @@
   },
   "devDependencies": {
     "codecov": "^3.0.4",
-    "eslint": "^5.1.0",
-    "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": "^3.6.2",