QtHelp Build: Update Sphinx issue URLs in comments
The QtHelp Sphinx generation code contains two links to Sphinx issues that used old, dead BitBucket URLs. Those issues were migrated to GitHub, so the dead links can be replaced with working ones.
The QtHelp Sphinx generation code contains two links to Sphinx issues that used old, dead BitBucket URLs. Those issues were migrated to GitHub, so the dead links can be replaced with working ones.