Update alecthomas/chroma to v2.16.0

[jamesponddotco]

While updating dependencies in #5, I noticed that we're using alecthomas/chroma v0.10.0 while v2.16.0 is out, which was an oversight on my part when I added the dependency to the service.

I need to investigate what is required to update chroma to v2.16.0.