add xml2json to travis requirements
add xml2json to travis requirements

puttarajubr/commcare-hq,dimagi/commcare-hq,qedsoftware/commcare-hq,qedsoftware/commcare-hq,puttarajubr/commcare-hq,SEL-Columbia/commcare-hq,SEL-Columbia/commcare-hq,puttarajubr/commcare-hq,puttarajubr/commcare-hq,dimagi/commcare-hq,SEL-Columbia/commcare-hq,qedsoftware/commcare-hq,dimagi/commcare-hq,qedsoftware/commcare-hq,dimagi/commcare-hq,dimagi/commcare-hq,qedsoftware/commcare-hq