Ignore index.d.ts when linting

[mschrage]

What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)
Bug fix
What is the current behavior? (You can also link to an open issue here)
See description #825
What is the new behavior (if this is a feature change)?
Linting no longer fails
Additional info:

[withfig-bot]

No files changed ☑️

[withfig-bot]

Hello @mschrage,
thank you very much for creating a Pull Request!
Here is a small checklist to get this PR merged as quickly as possible:

• Do all subcommands / options which take arguments include the args property (args: {})?
• Are all options modular? E.g. -a -u -x instead of -aux
• Have all other checks passed?

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