Widget state not saved or restored correctly on Demo notebook

[chrisperks]

Environment

• Operating System: Binder
• Python Version: 3
• How did you install Qgrid: Binder - online demo - https://notebooks.gesis.org/binder/jupyter/user/quantopian-qgrid-notebooks-id9a7fzi/notebooks/index.ipynb#

Description of Issue

• What did you expect to happen?

I can edit a cell in a QGrid table, refresh the page, and see my changes reflected in the table.

• What happened instead?

My changes are not visible immediately. If I click 'Add Row', then my changes are now visible.

Reproduction Steps

1. Load the QGrid demo page in Binder - https://notebooks.gesis.org/binder/jupyter/user/quantopian-qgrid-notebooks-id9a7fzi/notebooks/index.ipynb#
2. Execute the Example 1 cell and view the QGrid widget
3. Make a change to a cell - example, change D1 to read 'bar-boo-bam'

4. Select 'Save Notebook Widget State' from the Jupyter menu

5. Refresh page - changes are not visible. If I click 'Add Row', changes now appear.