Ported strings on generators.py file to Python 3 syntax.
Ported strings on generators.py file to Python 3 syntax.

oesteban/mriqc,poldracklab/mriqc,oesteban/mriqc,poldracklab/mriqc,poldracklab/mriqc,oesteban/mriqc,poldracklab/mriqc,oesteban/mriqc