Changes to make it build on dockerhub.

[marcelstoer]

Thanks! Would have a appreciated a brief a description to learn what the real issue is (inferred it from your commit message). This shows once again that Docker Hub isn't (yet) the great solution they claim it be:

• I wasn't notified that the last 3 builds failed, https://hub.docker.com/r/marcelstoer/nodemcu-build/builds/
• I was never notified that they changed the rules which made the builds fail in the first place
• (the mediocre commenting feature is still not fixed)

[mikeller]

Sorry for not being too verbose about it. I did the fix on my fork of your repo on GutHub, and then as an afterthought thought you might want to have it too.

As to why and what it fixes, I don't know, there doesn't seem to be much documentation on DockerHub. I just noticed that the version with sudo and -y was failing, googled around to see what others did, tried that, and it worked.

Thanks for your work anyway. The idea of providing a docker image as a cross platform build environment is great. I've borrowed it to do the same for another hobbyist project that I am involved in.