Zippy invocation broken on Linux / Debian 9.11 #174

The installer fails to extract the starterkit when running on Linux, tested on Debian 9.11.

Using a load of hacks in debugging I managed to expand the output from failed to extract the starterkit. easiest solution is to manually download it and copy <path>./dist</path to ./source/. to the real error message of Zippy:

Unable to execute the following command '/bin/tar' '--extract' '--file=/tmp/pl-sk/pl-sk-archive.tar.gzpfOkBu' '--overwrite-dir' '--overwrite' '--gzip' '--directory' '/tmp/pl-sk/pl-sk-archive' {output: /bin/tar: '--overwrite' cannot be used with '--overwrite-dir'
Try '/bin/tar --help' or '/bin/tar --usage' for more information.
}

I suggest replacing the Zippy invocation in core/src/PatternLab/Fetch.php with a plain old call to the tar binary. The starterkits are .tar.gz files anyway so there is no need at all for an abstraction library.