(PDB-3510) README.md: display travis status
(PDB-3510) README.md: display travis status

puppetlabs/puppetdb,puppetlabs/puppetdb,rbrw/puppetdb,rbrw/puppetdb,rbrw/puppetdb,mullr/puppetdb,mullr/puppetdb,rbrw/puppetdb,mullr/puppetdb,rbrw/puppetdb,puppetlabs/puppetdb,puppetlabs/puppetdb,mullr/puppetdb,mullr/puppetdb,puppetlabs/puppetdb