build: update dependencies to work with Node v10

Two dependencies, node-sass and fsevents, needed to be upgraded in order
to support Node v10. I used the `yarn why [package]` command to find out
which packages depend on them and used `yarn upgrade [package]` to
upgrade top-level packages which ultimately depend on them to the
highest version allowed by ranges specified package.json. The two
packages were webpack-atoms and babel-cli.

Fixes #335.

Author: silvenon