Add bundled gems to Gemfile

Author: yasulab

Gemfile

@@ -1,7 +1,6 @@
 source 'https://rubygems.org'
 
 gem 'jekyll'
-gem 'webrick'
 gem 'rake'
 
 group :jekyll_plugins do
@@ -12,3 +11,10 @@ end
 group :development, :test do
   gem 'html-proofer'
 end
+
+# Declare to install bundled gems to fix warnings:
+# https://www.ruby-lang.org/ja/news/2024/12/25/ruby-3-4-0-released/
+# https://www.ruby-lang.org/ja/news/2023/12/25/ruby-3-3-0-released/
+gem 'csv'
+gem 'base64'
+gem 'logger'