update broken dependencies

[geppy]

Update dependencies that have stopped working over time.

• node-sass is deprecated, and (via node-gyp) pulls in python2 (not available on modern systems). Fortunately, sass is a drop-in replacement for the purposes of this project.
• webpack@4's default hashing algorithm (MD4) is disabled by default in OpenSSL 3.0.0+ / Node 18+ (worked around via Add support for md4 in Node >=18. webpack/webpack#17628).