Update flag description (#120)
Update flag description (#120)

-ca-key and -ca-cert were changed to --signing-key and --signing-cert
here:
https://github.com/istio/auth/pull/59/files#diff-18dd05e4ee80822d7f159545a7e0dcf6R31
myidpt/auth,crazytan/auth,crazytan/auth,lookuptable/auth,wattli/auth,istio/old_auth_repo,wattli/auth,myidpt/auth,wattli/auth,lookuptable/auth,crazytan/auth,lookuptable/auth,istio/old_auth_repo,istio/old_auth_repo,myidpt/auth