Fix an encoding bug in the Kythe URI spec.
Fix an encoding bug in the Kythe URI spec.

Summary:
One of the examples showed "lang=c++" in a Kythe URI, but the "+"
characters should be percent-encoded.

Reviewers: shahms

Reviewed By: shahms

Differential Revision: https://phabricator-dot-kythe-repo.appspot.com/D787

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