Avoid installing gems for development on GitHub Actions

This fixes #14

Author: noraworld

Gemfile

@@ -6,7 +6,18 @@ ruby '3.1.1'
 
 gem 'faraday'
 
-group :development, :test do
+# For development
+#
+# These gems should be installed only for development environment, but
+# `bundle config set --local without 'development,test'` cannot be
+# used because it stores the configuration in `.bundle/config`, and
+# this file is hard to track on Git
+#
+# By the way, `--without` option is deprecated
+#
+# ENV['CI'] is only set on GitHub Actions
+#
+unless ENV['CI']
   gem 'dotenv'
   gem 'pry-byebug'
 end