Notebook cannot work with latest delta and old forge

I believe there was a change in Delta that prohibited the usage of top level properties starting with an underscore _.
Nexus Forge `nexus/docs/src/main/paradox/docs/getting-started/notebooks` should be using the latest nexus-forge release and not 0.7.0, because some data operations using nexus-forge will not work, because forge would send some properties starting in _

For example [this notebook](https://github.com/BlueBrain/nexus/blob/master/docs/src/main/paradox/docs/getting-started/notebooks/MOOC_Content_based_Recommender_System_using_Blue_Brain_Nexus.ipynb) would fail for doing something as simple as retrieving a resource and updating it.