We depend on a few packages for compiling JavaScript, namely Babel,

Uglify-JS, and LessCSS. Our dependencies were locked to specific

versions, meaning we weren't benefiting from any bug fixes or security

updates (less of a problem in our case, given that this is purely

compile time of our own media, but still worth avoiding).
We now specify the latest minor release in each series we use, and

specify that newer minor releases are also acceptable. Right now, this

only actually affects babel-cli, babel-preset-es2015, and

uglify-js.
We are not using the latest versions of each, for compatibility on

this branch. Review Board 4.0 upgrades to modern versions.

Built Djblets and Review Board packages successfully. Compared static

media files between the old and new packages, and there were no

substantial changes that I noted (just very slight differences in

minimization that don't affect any actual code).