Add changelog_uri to gemspec metadata

Adds a link to the GitHub Releases page for this gem consistent with other gems in the Ruby organization.

See-also: https://github.com/ruby/json/blob/master/json.gemspec
See-also: https://github.com/ruby/matrix/blob/master/matrix.gemspec
See-also: https://github.com/ruby/ostruct/blob/master/ostruct.gemspec
See-also: https://github.com/ruby/tsort/blob/master/tsort.gemspec

Author: jgarber623

benchmark.gemspec

@@ -20,6 +20,7 @@ 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.