[ci skip] Formatting changes.

Signed-off-by: Krzysztof Wilczynski <krzysztof.wilczynski@linux.com>
Force bundler to use single thread for building Ruby gems.

This is due to a bug, see: https://github.com/rubygems/rubygems/pull/1005

Signed-off-by: Krzysztof Wilczynski <krzysztof.wilczynski@linux.com>