ipywidgets 7.2.1, widgetsnbextension 3.2.1

This upgrades to the newest jupyterlab services package.

ipywidgets-7.2.1.tar.gz 
md5: 4eefd1b210020f27c8e384f50f98b9f8
sha1: 4f20d3394f026060ad374c1613d008a85846586c
sha256: ab9869cda5af7ba449d8f707b29b7e97a7db97d6366805d6b733338f51096f54

widgetsnbextension-3.2.1.tar.gz 
md5: 2b87b1461738f10c0d476b2e2aa8099d
sha1: 62f0a262bb36bd8fc25332707ba76bdf6f79b4b6
sha256: 5417789ee6064ff515fd10be24870660af3561c02d3d48b26f6f44285d0f70cc