use base64 for BSD systems where tr won't handle illegal characters (#174)
use base64 for BSD systems where tr won't handle illegal characters (#174)

The GNU version of 'tr' will ignore illegal characters, the BSD
version does not and will fail with 'illegal byte sequence'.
janetkuo/marketplace-k8s-app-tools,GoogleCloudPlatform/marketplace-k8s-app-tools,janetkuo/marketplace-k8s-app-tools,GoogleCloudPlatform/marketplace-k8s-app-tools