Container image not pulled from shub on profile `singularity`

Running the command 
```
nextflow run nf-core/hlatyping -profile singularity,test --outdir $PWD/results
```
locally, does not pull the container from Singularity Hub, but Docker Hub and result in extensive CPU usage in order to create the sqash Filesystem.

Expected behaviour:
Given the profile `singularity`, the container should be pulled from Singularity Hub directly.
