PsychToolbox download error!!!!

when I run DownloadPsychtoolbox('C:\My tool\'), after a while, I received errors saying that Unable to connect to a repository at: URL https://github.com/Psychtoolbox-3/Psychtoolbox3/branches/beta/Psychtoolbox

I also checked this link is not available. 

Could you please let us know how we can sort it out? 

Cheers,

Mary