fix #217: add `@typescript-eslint/parser` to deps

[tedbyron]

What is the purpose of this pull request?

[ ] Documentation update [ ] Bug fix [ ] New feature [X] Other, please explain:

What changes did you make?

added a single dependency - @typescript-eslint/parser because it is a peer dependency of @typescript-eslint/eslint-plugin. npm does not warn when installing ts-standard and will install @typescript-eslint/parser silently, but yarn will show a warning.

Which issue (if any) does this pull request address?

#217

Is there anything you'd like reviewers to focus on?

[welcome[bot]]

🙌 Thanks for opening this pull request! You're awesome.

[theoludwig]

Thanks for your contribution! @tedbyron We now include @typescript-eslint/parser in dependencies with this PR: https://github.com/standard/ts-standard/pull/254.