[FIX] Docker&conda interaction breaks singularity
[FIX] Docker&conda interaction breaks singularity

Closes #651. Reference https://github.com/singularityware/singularity/issues/571

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