fix: use pessimistic nokogiri version constraints

Address review feedback: replace open-ended >= 1.19.2 with pessimistic
constraints to prevent a hypothetical nokogiri 2.0 from being pulled in.

- gemspec: ~> 1.19.2 (allows 1.19.x patches, caps at < 1.20)
- Gemfile: ~> 1.19 (allows 1.19.x and 1.20.x, caps at < 2.0)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: zkoppert

Gemfile

@@ -15,4 +15,4 @@ gem "twitter-text", "~> 1.14"
 gem "asciidoctor", "~> 2.0.26"
 gem "rake"
 gem "rexml"
-gem "nokogiri", ">= 1.19.2"
+gem "nokogiri", "~> 1.19"

Gemfile.lock

@@ -126,7 +126,7 @@ DEPENDENCIES
   html-pipeline (~> 1.0)
   kramdown
   minitest (~> 5.4, >= 5.4.3)
-  nokogiri (>= 1.19.2)
+  nokogiri (~> 1.19)
   nokogiri-diff (~> 0.3.0)
   org-ruby (= 0.9.12)
   rake

github-markup.gemspec

@@ -25,7 +25,7 @@ Gem::Specification.new do |s|
   s.add_development_dependency 'minitest', '~> 5.4', '>= 5.4.3'
   s.add_development_dependency 'html-pipeline', '~> 1.0'
   s.add_development_dependency 'sanitize', '>= 4.6.3'
-  s.add_development_dependency 'nokogiri', '>= 1.19.2'
+  s.add_development_dependency 'nokogiri', '~> 1.19.2'
   s.add_development_dependency 'nokogiri-diff', '~> 0.3.0'
   s.add_development_dependency "github-linguist", ">= 7.1.3"
 end