chore(deps): update linters (#449)

Author: renovate[bot]

package.json

@@ -72,8 +72,8 @@
     "@types/tmp": "0.1.0",
     "assert-rejects": "^1.0.0",
     "codecov": "^3.5.0",
-    "eslint": "^5.16.0",
-    "eslint-config-prettier": "^5.0.0",
+    "eslint": "^6.0.0",
+    "eslint-config-prettier": "^6.0.0",
     "eslint-plugin-node": "^9.0.1",
     "eslint-plugin-prettier": "^3.1.0",
     "google-proto-files": "^1.0.0",