Update production-setup.md
Update production-setup.md

Yarn install in vue-storefront directory will fail if bzip2 not installed. Added a note to this effect.

Output:
PhantomJS not found on PATH
Downloading https://github.com/Medium/phantomjs/releases/download/v2.1.1/phantomjs-2.1.1-linux-x86_64.tar.bz2
Saving to /tmp/phantomjs/phantomjs-2.1.1-linux-x86_64.tar.bz2
Receiving...

Received 22866K total.
Extracting tar contents (via spawned process)
Error extracting archive
Phantom installation failed { Error: Command failed: tar jxf /tmp/phantomjs/phantomjs-2.1.1-linux-x86_64.tar.bz2
tar (child): bzip2: Cannot exec: No such file or directory
tar (child): Error is not recoverable: exiting now
tar: Child returned status 2
tar: Error is not recoverable: exiting now
DivanteLtd/vue-storefront,pkarw/vue-storefront,DivanteLtd/vue-storefront,pkarw/vue-storefront,pkarw/vue-storefront,DivanteLtd/vue-storefront,pkarw/vue-storefront,DivanteLtd/vue-storefront