build: bump linter versions and fix failure

[crisbeto]

Bumps to the latest versions of stylelint and tslint, and fixes a new failure.

[ngbot]

I see that you just added the pr: merge ready label, but the following checks are still failing:
     status "branch-manager" is failing

If you want your PR to be merged, it has to pass all the CI checks.

If you can't get the PR to a green state due to flakes or broken master, please try rebasing to master and/or restarting the CI job. If that fails and you believe that the issue is not due to your change, please contact the caretaker and ask for help.

[angular-automatic-lock-bot]

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