Minor Fix: Fixed Product Tag Arguments

Product Tags are labeled as non-hierarchical, but they are labeled with hierarchical labels instead of non-hierarchical labels. On the back-end everything shows up and works as intended. WordPress just ignores the mislabeled args and uses the correct ones by default. Always good to follow register_taxonomy() args :p.
Merge pull request #6239 from vlandfair/patch-1

Minor Fix: Fixed Product Tag Arguments