Build the correct plugin_loader.go when a plugin project is accessed via https+auth

This small change builds the correct plugin_loader.go when a plugin project is accessed via https+auth. 
Thanks for the contribution.
- To work properly with sub packages the replacement would need to happen in parse_url.
- The replacement should also conform to the userinfo grammar in RFC 3986 Appendix A; the expression above is far to restrictive.