add bcftools to travis setup
add bcftools to travis setup

kyleabeauchamp/pysam,kyleabeauchamp/pysam,TyberiusPrime/pysam,bioinformed/pysam,bioinformed/pysam,bioinformed/pysam,pysam-developers/pysam,TyberiusPrime/pysam,TyberiusPrime/pysam,kyleabeauchamp/pysam,bioinformed/pysam,pysam-developers/pysam,pysam-developers/pysam,TyberiusPrime/pysam,TyberiusPrime/pysam,kyleabeauchamp/pysam,bioinformed/pysam,pysam-developers/pysam,kyleabeauchamp/pysam