ENH: Updating SWIG superbuild to 2.0.12 official release

Change-Id: I5ba4eb4c35eb9ff5c2e4b3f796c8307b1f418d78
Merge topic 'SIMPLEITK-482_UpdateSWIGTo2.0.12' into next

96dda78f ENH: Updating SWIG superbuild to 2.0.12 official release