FIX: Participant labels starting with ``[sub]`` cannot be used
FIX: Participant labels starting with ``[sub]`` cannot be used

Resolves: #889.
poldracklab/mriqc,oesteban/mriqc,poldracklab/mriqc,oesteban/mriqc,poldracklab/mriqc,poldracklab/mriqc,oesteban/mriqc,oesteban/mriqc