Download a root certificate from the server and save it to a specified file path.
The path argument should include the file name and extension where the certificate will be stored.
For example, '/path/to/root.crt'. The recommended file extension for certificates is '.crt'.

alpacon authority download-crt [AUTHORITY ID] [flags]

	alpacon authority download-crt [AUTHORITY ID] --out=/path/to/root.crt

  -h, --help         help for download-crt
  -o, --out string   path where root certificate should be stored