Update README.md to use proper bug URL
While I was looking at this project, I noticed that the bug URL still pointed to Bugzilla, which seems to be closed for new bug reports.
This MR changes the bug URL to the Gitlab version.
Due to an influx of spam, we have had to impose restrictions on new accounts. Please see this wiki page for instructions on how to get full permissions. Sorry for the inconvenience.
While I was looking at this project, I noticed that the bug URL still pointed to Bugzilla, which seems to be closed for new bug reports.
This MR changes the bug URL to the Gitlab version.