Use a KRL for revoked certs

.travis.yml

cmd/cashierd/main.go

server/signer/signer.go

server/signer/signer_test.go

templates/certs.go

vendor/github.com/stripe/krl/LICENSE

vendor/github.com/stripe/krl/README.md

vendor/github.com/stripe/krl/format.go

vendor/github.com/stripe/krl/krl.go

vendor/github.com/stripe/krl/parse.go

vendor/vendor.json