Notebook loading error when opening dataframes.ipynb

Reproduction steps.

• Go to https://beam.apache.org/documentation/dsls/dataframes/overview/
• Click on the 'RUN IN COLAB' icon on the top
• The following error message will show up
• I verified only dataframes.ipynb has this issue under https://github.com/apache/beam/tree/master/examples/notebooks/tour-of-beam

Notebook loading error
There was an error loading this notebook. Ensure that the file is accessible and try again.Unexpected string in JSON at position 29287
https://github.com/apache/beam/blob/master/examples/notebooks/tour-of-beam/dataframes.ipynb