Bump tslint from 5.20.1 to 6.1.0 in /ui

Bumps [tslint](https://github.com/palantir/tslint) from 5.20.1 to 6.1.0.
- [Release notes](https://github.com/palantir/tslint/releases)
- [Changelog](https://github.com/palantir/tslint/blob/master/CHANGELOG.md)
- [Commits](palantir/tslint@5.20.1...6.1.0)

Signed-off-by: dependabot-preview[bot] <[email protected]>

Author: dependabot-preview[bot]

ui/package-lock.json

@@ -90,7 +90,7 @@
     "gh-pages": "^2.2.0",
     "prettier": "^1.18.2",
     "rimraf": "^3.0.2",
-    "tslint": "^5.20.1"
+    "tslint": "^6.1.0"
   },
   "pancake": {
     "auto-save": true,