Update module github.com/urfave/cli/v2 to v2.8.1

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change
github.com/urfave/cli/v2	require	patch	v2.8.0 -> v2.8.1

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Release Notes

urfave/cli

### [`v2.8.1`](https://togithub.com/urfave/cli/releases/tag/v2.8.1) [Compare Source](https://togithub.com/urfave/cli/compare/v2.8.0...v2.8.1) #### What's Changed - Run docs tests against current work tree by [@​meatballhat](https://togithub.com/meatballhat) in [https://github.com/urfave/cli/pull/1403](https://togithub.com/urfave/cli/pull/1403) - Remove GPL2 dependency introduced in v2.7.0 by [@​AkihiroSuda](https://togithub.com/AkihiroSuda) in [https://github.com/urfave/cli/pull/1405](https://togithub.com/urfave/cli/pull/1405) **Full Changelog**: https://github.com/urfave/cli/compare/v2.8.0...v2.8.1

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