Only pass -drf option in recent GATK (3.5+)
Only pass -drf option in recent GATK (3.5+)

Avoid errors on older GATK versions. Thanks to @scatreux

mjafin/bcbio-nextgen,a113n/bcbio-nextgen,a113n/bcbio-nextgen,biocyberman/bcbio-nextgen,vladsaveliev/bcbio-nextgen,lbeltrame/bcbio-nextgen,lbeltrame/bcbio-nextgen,mjafin/bcbio-nextgen,chapmanb/bcbio-nextgen,lbeltrame/bcbio-nextgen,brainstorm/bcbio-nextgen,vladsaveliev/bcbio-nextgen,a113n/bcbio-nextgen,biocyberman/bcbio-nextgen,vladsaveliev/bcbio-nextgen,mjafin/bcbio-nextgen,brainstorm/bcbio-nextgen,chapmanb/bcbio-nextgen,biocyberman/bcbio-nextgen,brainstorm/bcbio-nextgen,chapmanb/bcbio-nextgen