Regression in 3.2.0: syntax highlighting no longer works in new notebooks

[krassowski]

Description

Regression in 3.2.0: syntax highlighting no longer works in new notebooks

Reproduce

1. Run https://gist.github.com/krassowski/e05621c5d3a5e67779bb24d66fe8a783
2. See

Expected behavior

As before:

Context

Something about language_info in #355 probably