I just tried again from master and it compiles properly for me
GELU has only been added in master (not in 1.3.1). Make sure that you are using the python where the brand new pytorch is installed in.
Or build the 1.3.1 doc by first calling git checkout v1.3.1.
If you are on the master branch, you need to have a pytorch from the master branch installed. You can check with print(torch.__version__) in a command line.
If you have 1.3.1 installed, you will only be able to build the 1.3.1 doc.