Updating syntax and dependencies to match Atlas Workers Ruby version

While I was testing this locally, I noticed that there was still Ruby 2.x
era syntax in the scripts and spec files. I went ahead and updated those
and also set the Ruby version in the Gemfile to match what's on the Workers.

EDIT: Updating Ruby version in GitHub CI

Author: nadamsoreilly

.github/workflows/ci.yaml

@@ -19,7 +19,7 @@ jobs:
       - name: Set up Ruby
         uses: ruby/setup-ruby@v1
         with:
-          ruby-version: 3.1
+          ruby-version: 3.3.6
           bundler-cache: true
       - name: Run tests
         run: bundle exec rspec spec/htmlbook_spec.rb

Gemfile

@@ -1,4 +1,5 @@
 source 'https://rubygems.org'
+ruby "3.3.6"
 
 group :test do
   gem "asciidoctor"

Gemfile.lock

@@ -1,11 +1,11 @@
 GEM
   remote: https://rubygems.org/
   specs:
-    asciidoctor (2.0.17)
-    concurrent-ruby (1.1.10)
-    diff-lcs (1.6.0)
+    asciidoctor (2.0.23)
+    concurrent-ruby (1.3.5)
+    diff-lcs (1.6.1)
     mini_portile2 (2.8.8)
-    nokogiri (1.18.4)
+    nokogiri (1.18.7)
       mini_portile2 (~> 2.8.2)
       racc (~> 1.4)
     racc (1.8.1)
@@ -22,7 +22,7 @@ GEM
       diff-lcs (>= 1.2.0, < 2.0)
       rspec-support (~> 3.13.0)
     rspec-support (3.13.2)
-    tilt (1.4.1)
+    tilt (2.6.0)
 
 PLATFORMS
   ruby
@@ -34,5 +34,8 @@ DEPENDENCIES
   rspec
   tilt
 
+RUBY VERSION
+   ruby 3.3.6p108
+
 BUNDLED WITH
    2.4.19

scripts/convert_book.rb

@@ -4,7 +4,7 @@
 require 'fileutils'
 
 book_folder = ARGV[0]
-raise "Book Folder does not exist: #{book_folder}" unless File.exists?(book_folder)
+raise "Book Folder does not exist: #{book_folder}" unless File.exist?(book_folder)
 
 Dir.glob("#{book_folder}**/*.{asciidoc,adoc,asc}") do |file|
   puts "Converting #{File.basename(file)}"