Update Jekyll version support

[MichaelCurrin]

I noticed that your Gemfile only supports Jekyll 4.

There are differences between 3 and 4, notably in the way the {% link file.md %} tag operates.

If you project is intended to only work on Jekyll 4 (ie it will break on Jekyll 3), then I recommend you add a note in the readme saying it only works on Jekyll 4 and therefore will not work on GitHub Pages (which only supports 3).

On the other hand, if you have no material differences in your code, I suggest you downgrade to Jekyll 3.9 in your Gemfile. This means that your project will work as a expected on GH Pages. your project will have a wider reach (I think most Jekyll users are using GH Pages and not some custom setup). And also there will no surprises between locally Jekyll 4 and GH Pages Jekyll 3.

Here is a list of all the gems that GitHub Pages is pinned to. Your Gemfile cannot alter what gets used on GH Pages, so it is safest to rather update your Gemfile to be in sync in GH.

https://pages.github.com/versions/

[MichaelCurrin]

Sorry for the long message.

Here is my Gemfile in my template project for comparison.

https://github.com/MichaelCurrin/jekyll-blog-demo/blob/master/Gemfile