Out of date function reference in workflows.rst

[emdupre]

Currently, the workflows section on refinement of the brain mask points to an older fMRIPrep freesurfer interface. I believe this functionality has since been moved to niworkflows in the freesurfer RefineBrainMask interface.

I'm happy to update the reference, but I wanted to make sure my mapping was correct, first !

[mgxd]

Yeah, that looks right to me - nice catch!