Bugfixes for Docker and image downloading

[stollcri]

• Fix issue preventing docker-compose build from working (on MacOS Catalina)
• Fix issue downloading large image zip files (stream the download)

[manishs17]

Are the changes compatible with older MacOS versions ?

[stollcri]

Yes, they should be, but I can only test on the most current version

[manishs17]

okay, I would test on some of them before merging. Thanks for the contribution.

[claverru]

Helo @stollcri , @manishs17,

I've had problems building the image via Docker with:

FileNotFoundError: [Errno 2] No such file or directory: 'llvm-config'
[...]
ERROR: Failed building wheel for llvmlite

It was solved by changing python:3-5-slim to python:3.6-slim in the Dockerfile, as it's stated in installation instructions (Python 3.6).

I don't know if this is related, but could work.

Regards.