OpenSSL::X509::Certificate#sign returns self, so assignment is silly
For what we're doing, the x509 cert version is irrelevant
we just signed ca_cert with the key, why are we calling it serial.key ?
why are we saving ca_cert as DER encoded?
And why are we concatenating ca_cert and key again?
run verify before and after signing
clean up requires, add shebang
remove unneeded puts
and simplify the ca cert read