Bump tslint from 6.1.2 to 6.1.3 in /functions

Bumps [tslint](https://github.com/palantir/tslint) from 6.1.2 to 6.1.3.
- [Release notes](https://github.com/palantir/tslint/releases)
- [Changelog](https://github.com/palantir/tslint/blob/master/CHANGELOG.md)
- [Commits](palantir/tslint@6.1.2...6.1.3)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Author: dependabot-preview[bot]

functions/package-lock.json

@@ -24,7 +24,7 @@
   },
   "devDependencies": {
     "firebase-functions-test": "^0.2.1",
-    "tslint": "^6.1.2",
+    "tslint": "^6.1.3",
     "typescript": "^4.0.2"
   },
   "private": true