Add Travis build status to README
Add Travis build status to README

dpattmann/knife-vsphere,adamleff/knife-vsphere,swalberg/knife-vsphere,mheidenr/knife-vsphere,swalberg/knife-vsphere,ezrapagel/knife-vsphere,rhadoo/knife-vsphere,CoreMedia/knife-vsphere,chef-partners/knife-vsphere,DennisBP/knife-vsphere