Upgrade to LESS 3.9.0
Review Request #10427 — Created Feb. 22, 2019 and submitted — Latest diff uploaded
This change upgrades us to the latest LESS version for the Djblets
1.0/Review Board 3.0 series. This matches a change which was already
done for 2.0/4.0.
- Verified that stylesheets still compiled correctly.
- Built the djblets package.