Julia 0.6.0 not available on Windows

[ufechner7]

On Linux I can do:

juliup add 0.6.0

This does not work on Windows:

juliaup add 0.6.0
Error: '0.6.0' is not a valid Julia version or channel name.

It would be better if older Julia versions would also be available on Windows to be able to make old Julia programs work before starting to port them to newer Julia versions.