[ruby/net-protocol] Provide a 'Changelog' link on rubygems.org/gems/net-protocol

By providing a 'changelog_uri' in the metadata of the gemspec
a 'Changelog' link will be shown on https://rubygems.org/gems/net-protocol
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/

https://github.com/ruby/net-protocol/commit/46e78a2a0a

lib/net/net-protocol.gemspec

@@ -21,6 +21,7 @@ Gem::Specification.new do |spec|
 
   spec.metadata["homepage_uri"] = spec.homepage
   spec.metadata["source_code_uri"] = spec.homepage
+  spec.metadata["changelog_uri"] = spec.homepage + "/releases"
 
   # Specify which files should be added to the gem when it is released.
   # The `git ls-files -z` loads the files in the RubyGem that have been added into git.