Gemfile Update suggestion for jekyll version 4.3.1

I'm using your nice template as a jekyll site builder rather than through github pages automatic (which is seriously behind on jekyll and rouge versions). The gem 'github-pages' prevents using newer versions. For me it was very difficult to figure everything out and get it working with more up to date versions, but that is because I've tried to skate on the entire ruby/gems/jekyll stack without ever learning how it works. I fumbled through to the following Gemfile which works for me. This version of jekyll allows rouge v4.0.0 which is what I really needed. It will of course not work like you expect if using github pages directly.

```
# frozen_string_literal: true

source "https://rubygems.org"
# gem "rails"
gem "jekyll", "~> 4.3.1"
group :jekyll_plugins do
gem "jekyll-paginate"
end
#gem 'github-pages', group: :jekyll_plugins
```