tensorflow issues with latest RStudio version

[njtierney]

Python is currently not detected - see issue discussed here: rstudio/reticulate#1062

[njtierney]

Current workaround is that you need to run

Sys.unsetenv("RETICULATE_PYTHON")

Before running library(greta) in a session.

Will need to see if we can set this up to run onload, perhaps, and if that interferes with installation