Setting up gemfile for Jekyll - unclear what is wrong - jekyll

Question

I'm trying to setup a gh-pages site with Jekyll.
When running jekyll server I run into the following error message:
10: from /Users/a56z/.rbenv/versions/2.6.3/bin/jekyll:23:in `<main>'
9: from /Users/a56z/.rbenv/versions/2.6.3/bin/jekyll:23:in `load'
8: from /Users/a56z/.rbenv/versions/2.6.3/lib/ruby/gems/2.6.0/gems/jekyll-4.0.0/exe/jekyll:11:in `<top (required)>'
7: from /Users/a56z/.rbenv/versions/2.6.3/lib/ruby/gems/2.6.0/gems/jekyll-4.0.0/lib/jekyll/plugin_manager.rb:52:in `require_from_bundler'
6: from /Users/a56z/.gem/ruby/2.6.0/gems/bundler-2.0.2/lib/bundler.rb:107:in `setup'
5: from /Users/a56z/.gem/ruby/2.6.0/gems/bundler-2.0.2/lib/bundler/runtime.rb:26:in `setup'
4: from /Users/a56z/.gem/ruby/2.6.0/gems/bundler-2.0.2/lib/bundler/runtime.rb:26:in `map'
3: from /Users/a56z/.gem/ruby/2.6.0/gems/bundler-2.0.2/lib/bundler/spec_set.rb:148:in `each'
2: from /Users/a56z/.gem/ruby/2.6.0/gems/bundler-2.0.2/lib/bundler/spec_set.rb:148:in `each'
1: from /Users/a56z/.gem/ruby/2.6.0/gems/bundler-2.0.2/lib/bundler/runtime.rb:31:in `block in setup'
/Users/a56z/.gem/ruby/2.6.0/gems/bundler-2.0.2/lib/bundler/runtime.rb:319:in `check_for_activated_spec!': You have already activated i18n 1.6.0, but your Gemfile requires i18n 0.9.5. Prepending `bundle exec` to your command may solve this. (Gem::LoadError) ```
My Gemfile looks as follows:
# Hello! This is where you manage which Jekyll version is used to run.
# When you want to use a different version, change it below, save the
# file and run `bundle install`. Run Jekyll with `bundle exec`, like so:
#
# bundle exec jekyll serve
gem 'github-pages'
#
# This will help ensure the proper Jekyll version is running.
# Happy Jekylling!
source 'https://rubygems.org'
gem 'jekyll', '3.8.6'
group :jekyll_plugins do
gem 'jekyll-feed'
gem 'jekyll-seo-tag'
end```
Please advise what I'm missing, I've been searching the web but couldn't find anything to make this work.
Also running bundle exec jekyll server doesn't work
I have also simplified the gemfile to this:
gem "jekyll"
gem "minima"
group :jekyll_plugins do
gem "jekyll-feed"
end
but even like so I get this error:
Configuration file: /Users/a56z/code/a56z/blog/my_pytter_blog/_config.yml
Source: /Users/a56z/code/a56z/blog/my_pytter_blog
Destination: /Users/a56z/code/a56z/blog/my_pytter_blog/_site
Incremental build: disabled. Enable with --incremental
Generating...
Jekyll Feed: Generating feed for posts
done in 0.229 seconds.
Auto-regeneration: enabled for '/Users/a56z/code/a56z/blog/my_pytter_blog'
bundler: failed to load command: jekyll (/Users/a56z/.rbenv/versions/2.6.3/bin/jekyll)
Errno::EADDRINUSE: Address already in use - bind(2) for 127.0.0.1:4000
/Users/a56z/.rbenv/versions/2.6.3/lib/ruby/2.6.0/socket.rb:201:in `bind'
/Users/a56z/.rbenv/versions/2.6.3/lib/ruby/2.6.0/socket.rb:201:in `listen'
/Users/a56z/.rbenv/versions/2.6.3/lib/ruby/2.6.0/socket.rb:764:in `block in tcp_server_sockets'
/Users/a56z/.rbenv/versions/2.6.3/lib/ruby/2.6.0/socket.rb:227:in `each'
/Users/a56z/.rbenv/versions/2.6.3/lib/ruby/2.6.0/socket.rb:227:in `foreach'
/Users/a56z/.rbenv/versions/2.6.3/lib/ruby/2.6.0/socket.rb:762:in `tcp_server_sockets'
/Users/a56z/.rbenv/versions/2.6.3/lib/ruby/2.6.0/webrick/utils.rb:65:in `create_listeners'
/Users/a56z/.rbenv/versions/2.6.3/lib/ruby/2.6.0/webrick/server.rb:127:in `listen'
/Users/a56z/.rbenv/versions/2.6.3/lib/ruby/2.6.0/webrick/server.rb:108:in `initialize'
/Users/a56z/.rbenv/versions/2.6.3/lib/ruby/2.6.0/webrick/httpserver.rb:47:in `initialize'
/Users/a56z/.rbenv/versions/2.6.3/lib/ruby/gems/2.6.0/gems/jekyll-4.0.0/lib/jekyll/commands/serve.rb:215:in `new'
/Users/a56z/.rbenv/versions/2.6.3/lib/ruby/gems/2.6.0/gems/jekyll-4.0.0/lib/jekyll/commands/serve.rb:215:in `start_up_webrick'
/Users/a56z/.rbenv/versions/2.6.3/lib/ruby/gems/2.6.0/gems/jekyll-4.0.0/lib/jekyll/commands/serve.rb:102:in `process'
/Users/a56z/.rbenv/versions/2.6.3/lib/ruby/gems/2.6.0/gems/jekyll-4.0.0/lib/jekyll/command.rb:89:in `block in process_with_graceful_fail'
/Users/a56z/.rbenv/versions/2.6.3/lib/ruby/gems/2.6.0/gems/jekyll-4.0.0/lib/jekyll/command.rb:89:in `each'
/Users/a56z/.rbenv/versions/2.6.3/lib/ruby/gems/2.6.0/gems/jekyll-4.0.0/lib/jekyll/command.rb:89:in `process_with_graceful_fail'
/Users/a56z/.rbenv/versions/2.6.3/lib/ruby/gems/2.6.0/gems/jekyll-4.0.0/lib/jekyll/commands/serve.rb:86:in `block (2 levels) in init_with_program'
/Users/a56z/.rbenv/versions/2.6.3/lib/ruby/gems/2.6.0/gems/mercenary-0.3.6/lib/mercenary/command.rb:220:in `block in execute'
/Users/a56z/.rbenv/versions/2.6.3/lib/ruby/gems/2.6.0/gems/mercenary-0.3.6/lib/mercenary/command.rb:220:in `each'
/Users/a56z/.rbenv/versions/2.6.3/lib/ruby/gems/2.6.0/gems/mercenary-0.3.6/lib/mercenary/command.rb:220:in `execute'
/Users/a56z/.rbenv/versions/2.6.3/lib/ruby/gems/2.6.0/gems/mercenary-0.3.6/lib/mercenary/program.rb:42:in `go'
/Users/a56z/.rbenv/versions/2.6.3/lib/ruby/gems/2.6.0/gems/mercenary-0.3.6/lib/mercenary.rb:19:in `program'
/Users/a56z/.rbenv/versions/2.6.3/lib/ruby/gems/2.6.0/gems/jekyll-4.0.0/exe/jekyll:15:in `<top (required)>'
/Users/a56z/.rbenv/versions/2.6.3/bin/jekyll:23:in `load'
/Users/a56z/.rbenv/versions/2.6.3/bin/jekyll:23:in `<top (required)>'