Fix the source relationship type for core-properties
Fix the source relationship type for core-properties

The URL wasn't quite right here, causing validation problems. See page 165
of ISO/IEC 29500-1:2008 for details.

Signed-off-by: Dan McGee <a6e5737275ff1276377ee261739f3ee963671241@gmail.com>

mikemaccana/python-docx,adnelson/docx-text-replacement,tomchipchase/python-docx,mouthwateringmedia/python-docx,firebitsbr/python-docx,toshka/python-docx,psquickitprageet/python-docx,adnelson/docx-text-replacement