`repo-style-checker`: Use an upstream version of yamllint

Now that [this pull request](https://github.com/adrienverge/yamllint/pull/630) has been merged, `repo-style-checker` can be updated in order to use the upstream yamllint repo instead of [my yamllint-pr repo](https://github.com/Jayman2000/yamllint-pr).