update gitignore to exclude dist and zipped man pages
update gitignore to exclude dist and zipped man pages

These are files generated when building releases, that should not be tracked.

SylvainCorlay/ipywidgets,ipython/ipywidgets,jupyter-widgets/ipywidgets,ipython/ipywidgets,SylvainCorlay/ipywidgets,ipython/ipywidgets,cornhundred/ipywidgets,jupyter-widgets/ipywidgets,ipython/ipywidgets,ipython/ipywidgets,cornhundred/ipywidgets,cornhundred/ipywidgets,cornhundred/ipywidgets,SylvainCorlay/ipywidgets,jupyter-widgets/ipywidgets,SylvainCorlay/ipywidgets,jupyter-widgets/ipywidgets,cornhundred/ipywidgets