Ignore pkg directory.
Ignore pkg directory.

This commit modifies .gitingore to ignore changes to the pkg directory
used when building Forge releases.

puppetlabs/puppetlabs-apt,gizmoguy/puppetlabs-apt,zoide/puppet-apt,gwdg/puppetlabs-apt,imphil/puppetlabs-apt,imphil/puppetlabs-apt