docker: fix permission issues in Dockerfile

[dvdksn]

I think the --link option might've caused a permission issue for the non-root hugo user.

Related issues:

• docker: npm errors (linux) #12970
• docker: npm errors (windows) #12971

Also noticed that the /project workdir was created before we assumed the hugo:hugo user, which resulted in that directory being owned by root. I reordered the instructions to make sure /project is owned by the correct user.

[dvdksn]

@jmooring @bep could you try with this build? I ran the reproducer in the linked issue (on macos) and it seems to work for me.

mkdir -p $HOME/.cache/hugo_cache
git clone https://github.com/jmooring/hugo-docker-test
cd hugo-docker-test
docker run --rm -v .:/project -v $HOME/.cache/hugo_cache:/cache -p 1313:1313 davidkarlsson416/hugo:12975 server --bind="0.0.0.0"

[bep]

Works for me.

[bep]

@dvdksn could you get the commit message(s) in line with the guidelines?