Bump tslint from 5.18.0 to 5.20.0

Bumps [tslint](https://github.com/palantir/tslint) from 5.18.0 to 5.20.0.
- [Release notes](https://github.com/palantir/tslint/releases)
- [Changelog](https://github.com/palantir/tslint/blob/master/CHANGELOG.md)
- [Commits](palantir/tslint@5.18.0...5.20.0)

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

package.json

@@ -38,7 +38,7 @@
     "devDependencies": {
         "@types/mocha": "^5.2.7",
         "@types/node": "^12.6.2",
-        "tslint": "^5.18.0",
+        "tslint": "^5.20.0",
         "typescript": "^3.5.3",
         "vscode": "^1.1.35"
     },