Log Message:
py-nbconvert: updated to 5.6.1

5.6.1:

Significant Changes
RegExRemove applies to all cells
RegExRemove preprocessor now removes cells regardless of cell outputs. Before \ 
this only cells that had outputs were filtered.

Comprehensive notes

New Features
- Add support for alt tags for jpeg and png images
- Allow HTML header anchor text to be HTML
- Change RegExRemove to remove code cells with output
- Added cell tag data attributes to HTML exporter

Fixing Problems
- Update svg2pdf.py to search the PATH for inkscape
- Fix latex dependencies installation command for Ubuntu systems

Testing, Docs, and Builds
- Added Circle CI builds for documentation
- Fix typo in argument name in docstring (TagRemovePreprocessor)
- Changelog typo fix
- Updated API page for TagRemovePreprocessor and TemplateExporter
- Added remove_input_tag traitlet to the docstring