Remove nbformat dependency from ipywidgets jupyter-widgets#3418

Author: Anthony Alvarez

python/ipywidgets/setup.cfg

@@ -32,13 +32,10 @@ zip_safe = False
 # include_package_data = True
 packages = find:
 
-# Requiring nbformat to specify bugfix version which is not required by
-# notebook - perhaps not needed anymore?
 install_requires =
   ipykernel>=4.5.1
   ipython>=6.1.0
   traitlets>=4.3.1
-  nbformat>=4.2.0
   widgetsnbextension~=4.0rc0
   jupyterlab_widgets~=3.0rc0