Repo2docker: Improve Julia handling so an environment.yml is not required

[yuvipanda]

Since otherwise the conda buildpack doesn't get triggered, and we require that right now.

[choldgraf]

note: requires at least an empty environment.yml file to work. It'll still work if you have a filled environment.yml file :-)

[willingc]

165 closes this issue. Please see https://github.com/binder-examples/julia-python for a helpful example for using Julia.

[yuvipanda]

Unfortunately, I think this is still a bug - we shouldn't need an empty environment file for julia to work. Documenting it is a great first step, since that unblocks people. However, this is a bug in our Julia buildpack we should fix.

@willingc is it ok if I re-open this?

[willingc]

Done. Renaming issue to be more clear. Thanks @yuvipanda.

[willingc]

Feel free to modify as needed @yuvipanda @choldgraf. 👍

[yuvipanda]

Once #213 is merged I think it will be no longer required!

[choldgraf]

as #213 is merged, I believe we can close this now!