Go mod vendor

Signed-off-by: Shengjing Zhu <zhsj@debian.org>

vendor/github.com/urfave/cli/CONTRIBUTING.md

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+## Contributing
+
+Use @urfave/cli to ping the maintainers.
+
+Feel free to put up a pull request to fix a bug or maybe add a feature. We will
+give it a code review and make sure that it does not break backwards
+compatibility. If collaborators agree that it is in line with
+the vision of the project, we will work with you to get the code into
+a mergeable state and merge it into the master branch.
+
+If you have contributed something significant to the project, we will most
+likely add you as a collaborator. As a collaborator you are given the ability
+to merge others pull requests. It is very important that new code does not
+break existing code, so be careful about what code you do choose to merge.
+
+If you feel like you have contributed to the project but have not yet been added
+as a collaborator, we probably forgot to add you :sweat_smile:. Please open an
+issue!