Provide a 'Changelog' link on rubygems.org/gems/diff-lcs

By providing a 'changelog_uri' in the metadata of the gemspec a
'Changelog' link will be shown on https://rubygems.org/gems/diff-lcs
which makes it quick and easy for someone to check on the changes
introduced with a new version.

Details of this functionality can be found on https://guides.rubygems.org/specification-reference/

diff-lcs.gemspec

@@ -6,7 +6,7 @@ Gem::Specification.new do |s|
   s.version = "1.5.1".freeze
 
   s.required_rubygems_version = Gem::Requirement.new(">= 0".freeze) if s.respond_to? :required_rubygems_version=
-  s.metadata = { "bug_tracker_uri" => "https://github.com/halostatue/diff-lcs/issues", "homepage_uri" => "https://github.com/halostatue/diff-lcs", "rubygems_mfa_required" => "true", "source_code_uri" => "https://github.com/halostatue/diff-lcs" } if s.respond_to? :metadata=
+  s.metadata = { "bug_tracker_uri" => "https://github.com/halostatue/diff-lcs/issues", "changelog_uri" => "https://github.com/mark-young-atg/diff-lcs/blob/main/History.md", "homepage_uri" => "https://github.com/halostatue/diff-lcs", "rubygems_mfa_required" => "true", "source_code_uri" => "https://github.com/halostatue/diff-lcs" } if s.respond_to? :metadata=
   s.require_paths = ["lib".freeze]
   s.authors = ["Austin Ziegler".freeze]
   s.date = "2024-01-31"