SimpleITK>=2.0.2 fails to open nii files

[patricio-astudillo]

When installing hd-bet from github, the requirement file states SimpleITK>=2.0.2 and this (currently) installs SimpleITK 2.1.1.2.

This version of SimpleITK fails to open *.nii.gz files. I already mentioned this in a previous issue but this was overwritten.

Fix: SimpleITK==2.0.2 works fine.

https://github.com/MIC-DKFZ/HD-BET/blob/56c7fb8e6509563aa6377cdb0f2dd4e7ad359252/requirements.txt#L4