Cap the Pygments dependency at < 2.6.
Review Request #10983 — Created March 31, 2020 and submitted
Pygments dropped Python 2 support with Pygments 2.6. While it might
still currently work on 2.6, we don't want to risk future versions
This change caps our dependency for Review Board 3.0 at < 2.6.
Uninstalled Pygments and re-ran
./setup.py develop. Verified it
installed Pygments 2.5.2 (the latest Python 2.x release).