This updates us to the latest versions of the following packages from

npm:

@babel/cli
@babel/core
@babel/present-env
babel-plugin-django-gettext
less
uglify-js

Most of these just bump to the latest minor/patch versions for each

package. The uglify-js patch is important for resolving local build

issues on Review Board 5 beta 1.
less got a major version bump, from ^3.11.0 to ^4.1.3. This is

compatible. The 4.x series mostly fixes some bugs and produces better

expected output for media queries when using certain operators like

division that are part of the syntax of the media query.

Successfully built Djblets, Review Board, and Power Pack static media,

without any noticeable regressions in styling.