Fix ReadtheDocs Documentation builds

[andersy005]

I noticed that the documentation builds on RTD have been failing for the last few months due to the Command killed due to excessive memory consumption error. This is due to the fact that conda consumes a lot of memory, and Readthedocs sets a limit to how much memory can be use. One can request memory increase for a project by contacting the RTD (Readthedocs) via https://github.com/readthedocs/readthedocs.org/issues

[gustavo-marques]

Thanks, @andersy005 ! I've requested a memory increase for this project.

readthedocs/readthedocs.org#6835