updated dockerfile to make patching local code for niworkflows easier
updated dockerfile to make patching local code for niworkflows easier

oesteban/preprocessing-workflow,poldracklab/preprocessing-workflow,shoshber/fmriprep,oesteban/preprocessing-workflow,shoshber/fmriprep,oesteban/fmriprep,poldracklab/fmriprep,oesteban/fmriprep,poldracklab/fmriprep,oesteban/fmriprep,poldracklab/preprocessing-workflow,poldracklab/fmriprep,chrisfilo/fmriprep