Use an updated version of ruby

With this configuration, it always uses an updated version of ruby and bundler
is the one which manages version of the dependencies, hence working in all
environments. Before, dependencies could not be satisfied in updated
environments because of bundler being too new.

_config.yml

@@ -1,26 +1,56 @@
 # Welcome to Jekyll!
 #
 # This config file is meant for settings that affect your whole blog, values
-# which you are expected to set up once and rarely need to edit after that.
+# which you are expected to set up once and rarely edit after that. If you find
+# yourself editing this file very often, consider using Jekyll's data files
+# feature for the data you need to update frequently.
+#
 # For technical reasons, this file is *NOT* reloaded automatically when you use
-# 'jekyll serve'. If you change this file, please restart the server process.
-
+# 'bundle exec jekyll serve'. If you change this file, please restart the server process.
+#
+# If you need help with YAML syntax, here are some quick references for you: 
+# https://learn-the-web.algonquindesign.ca/topics/markdown-yaml-cheat-sheet/#yaml
+# https://learnxinyminutes.com/docs/yaml/
+#
 # Site settings
+# These are used to personalize your new site. If you look in the HTML files,
+# you will see them accessed via {{ site.title }}, {{ site.email }}, and so on.
+# You can create any custom variable you would like, and they will be accessible
+# in the templates via {{ site.myvariable }}.
+
 title: Example Jekyll site using GitLab Pages
 email: your-email@domain.com
-description: > # this means to ignore newlines until "baseurl:"
+description: >- # this means to ignore newlines until "baseurl:"
   Write an awesome description for your new site here. You can edit this
   line in _config.yml. It will appear in your document head meta (for
   Google search results) and in your feed.xml site description.
 baseurl: "/jekyll" # the subpath of your site, e.g. /blog
-url: "/" # the base hostname & protocol for your site
+url: "/" # the base hostname & protocol for your site, e.g. http://example.com
 twitter_username: jekyllrb
 github_username:  jekyll
 gitlab_username:  pages
 
-# Outputting
-permalink: /:categories/:year/:month/:day/:title
-
 # Build settings
-markdown: kramdown
-exclude: ["README.md"]
+theme: minima
+plugins:
+  - jekyll-feed
+
+# Exclude from processing.
+# The following items will not be processed, by default.
+# Any item listed under the `exclude:` key here will be automatically added to
+# the internal "default list".
+#
+# Excluded items can be processed by explicitly listing the directories or
+# their entries' file path in the `include:` list.
+#
+# exclude:
+#   - .sass-cache/
+#   - .jekyll-cache/
+#   - gemfiles/
+#   - Gemfile
+#   - Gemfile.lock
+#   - node_modules/
+#   - vendor/bundle/
+#   - vendor/cache/
+#   - vendor/gems/
+#   - vendor/ruby/