loader: Use assign when loading variant sequences
loader: Use assign when loading variant sequences

For consistency with the reference loader, use assign() instead of an
explicit for loop when loading variant database sequences.

NVlabs/firepony,NVlabs/firepony,NVlabs/firepony,NVlabs/firepony,broadinstitute/firepony,broadinstitute/firepony,broadinstitute/firepony,broadinstitute/firepony