-Specifies a keyserver to provide the GPG key. Valid options: a string containing a domain name or a full URL (http://, https://, or
-hkp://).
+Specifies a keyserver to provide the GPG key. Valid options: a string containing a domain name or a full URL (http://, https://,
+hkp:// or hkps://). The hkps:// protocol is currently only supported on Ubuntu 18.04.