Building came across Extension error

[Mdnaimulislam]

Temporarily fixed it by changing the cache to force in the following block of the _config.yml file. (This takes around 14 minutes to run the whole jupyter book, which is reasonable)

execute:
execute_notebooks: force

There are two threads to watch for future updates on this issue.

1. Building came across Extension error jupyter-book/jupyter-book#1902
2. Pin jupyter_server<2 to fix build ProjectPythia/physical-oceanography-cookbook#35