Log Message:
py-nbconvert: updated to 5.4.1

5.4.1:
New Features
- Expose pygments styles
- Tornado 6.0 support -- Convert proxy handler from callback to coroutine
- Add option to overwrite the highlight_code filter

Fixing Problems
- Mathjax.tpl fix for rendering Latex in html
- Backwards compatbility for empty kernel names

Testing, Docs, and Builds
- DOC: Add missing language specification to code-block