Revert "Update url of issue tracker."

This reverts commit 082b634.

Author: hsbt

README.md

@@ -54,7 +54,7 @@ To install this gem onto your local machine, run `bundle exec rake install`. To
 
 ## Contributing
 
-Bug reports and Patch are welcome on https://bugs.ruby-lang.org/.
+Bug reports and pull requests are welcome on GitHub at https://github.com/ruby/webrick.
 
 ## License