add a missing PyYAML dependency
add a missing PyYAML dependency

mpurzynski/MozDef,jeffbryner/MozDef,jeffbryner/MozDef,mozilla/MozDef,mozilla/MozDef,mozilla/MozDef,jeffbryner/MozDef,mpurzynski/MozDef,mpurzynski/MozDef,mpurzynski/MozDef,mozilla/MozDef,jeffbryner/MozDef