Update module github.com/urfave/cli/v2 to v2.8.0

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change
github.com/urfave/cli/v2	require	minor	v2.7.1 -> v2.8.0

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Release Notes

urfave/cli

### [`v2.8.0`](https://togithub.com/urfave/cli/releases/tag/v2.8.0) [Compare Source](https://togithub.com/urfave/cli/compare/v2.7.2...v2.8.0) #### What's Changed - Add flag category support ([#​796](https://togithub.com/urfave/cli/issues/796)) by [@​michaeljs1990](https://togithub.com/michaeljs1990) / [@​meatballhat](https://togithub.com/meatballhat) in [https://github.com/urfave/cli/pull/1368](https://togithub.com/urfave/cli/pull/1368) - Introduce override hooks for suggestions by [@​meatballhat](https://togithub.com/meatballhat) in [https://github.com/urfave/cli/pull/1396](https://togithub.com/urfave/cli/pull/1396) - Point to the docs tree and site from top-level README by [@​meatballhat](https://togithub.com/meatballhat) in [https://github.com/urfave/cli/pull/1399](https://togithub.com/urfave/cli/pull/1399) **Full Changelog**: https://github.com/urfave/cli/compare/v2.7.2...v2.8.0 ### [`v2.7.2`](https://togithub.com/urfave/cli/releases/tag/v2.7.2) [Compare Source](https://togithub.com/urfave/cli/compare/v2.7.1...v2.7.2) #### What's Changed - Auto-detect zsh via `SHELL` ([#​1218](https://togithub.com/urfave/cli/issues/1218)) by [@​z0rc](https://togithub.com/z0rc) / [@​meatballhat](https://togithub.com/meatballhat) in [https://github.com/urfave/cli/pull/1350](https://togithub.com/urfave/cli/pull/1350) - Merging mostynb report source of parse errors by [@​meatballhat](https://togithub.com/meatballhat) in [https://github.com/urfave/cli/pull/1354](https://togithub.com/urfave/cli/pull/1354) - Report the source of a value when we cannot parse it by [@​mostynb](https://togithub.com/mostynb) in [https://github.com/urfave/cli/pull/1168](https://togithub.com/urfave/cli/pull/1168) - Add a security policy document by [@​meatballhat](https://togithub.com/meatballhat) in [https://github.com/urfave/cli/pull/1365](https://togithub.com/urfave/cli/pull/1365) **Full Changelog**: https://github.com/urfave/cli/compare/v2.7.1...v2.7.2

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