Fix a heading in the schema source.
Fix a heading in the schema source.

Summary:
Apparently ASCIIdoc doesn't treat something as a heading if its undermark is a
different length than the heading text. Fortunately, there was only one that
had this problem.

Reviewers: #core_team, shahms

Reviewed By: #core_team, shahms

Differential Revision: https://phabricator-dot-kythe-repo.appspot.com/D1270

kythe/kythe,kythe/kythe,kythe/kythe,legrosbuffle/kythe,legrosbuffle/kythe,bzz/kythe,benjyw/kythe,kythe/kythe,bzz/kythe,benjyw/kythe,kythe/kythe,legrosbuffle/kythe,legrosbuffle/kythe,bzz/kythe,benjyw/kythe,kythe/kythe,bzz/kythe,kythe/kythe,benjyw/kythe,legrosbuffle/kythe,benjyw/kythe,bzz/kythe,kythe/kythe,legrosbuffle/kythe,kythe/kythe,legrosbuffle/kythe,bzz/kythe,legrosbuffle/kythe,bzz/kythe,benjyw/kythe,legrosbuffle/kythe,kythe/kythe,bzz/kythe,benjyw/kythe,bzz/kythe,bzz/kythe,benjyw/kythe,legrosbuffle/kythe,benjyw/kythe,benjyw/kythe,bzz/kythe,benjyw/kythe,benjyw/kythe,kythe/kythe,legrosbuffle/kythe,bzz/kythe