use "-s" from docker_extract to build singularity images

tars-cwl-runner.sh

@@ -10,7 +10,7 @@ source ${toil_venv}/bin/activate
 export SINGULARITY_PULLFOLDER=${singularity_imgs_path}
 
 # Prefetch every docker images and built them for singularity
-docker_extract.py ${singularity_imgs_path} $1
+docker_extract.py -s ${singularity_imgs_path} $1
 
 # Run toil
 # export TOIL_SLURM_ARGS=""  # Need to be set by parameters later