Need newline after changes list

tool/gen-github-release.rb

@@ -51,7 +51,7 @@ notes.uniq!
 
 note << notes.join("\n")
 
-note << "\n"
+note << "\n\n"
 note << "Note: This list is automatically generated by tool/gen-github-release.rb. Because of this, some commits may be missing.\n\n"
 note << "## Full Changelog\n\n"
 note << "https://github.com/ruby/ruby/compare/#{ARGV[0]}...#{ARGV[1]}\n\n"