Fix typos in GitHub Pages around Jekyll

[tnir]

Why:

Typos could be a blocker for readers.

What's being changed:

Fixes typos in GitHub Pages around Jekyll.

Confirmed at the following pages on review apps:

• https://docs-687--typos-in-working-wit.herokuapp.com/en/free-pro-team@latest/github/working-with-github-pages/about-github-pages-and-jekyll#about-jekyll
• https://docs-687--typos-in-working-wit.herokuapp.com/en/free-pro-team@latest/github/working-with-github-pages/setting-a-markdown-processor-for-your-github-pages-site-using-jekyll

Check off the following:

• All of the tests are passing.
• I have reviewed my changes in staging.
• For content changes, I have reviewed the localization checklist
• For content changes, I have reviewed the Content style guide for GitHub Docs.

[janiceilene]

Thanks so much for the fixes @tnir 🙌 I'll update this branch and get it merged once tests are green 🍏

[github-actions]

Thanks very much for contributing! Your pull request has been merged 🎉 You should see your changes appear on the site in approximately 24 hours.