referene: fix formatting of "deprecated" comment.

Go requires "deprecated" comments to have an empty line before them,
and to not be all-caps.

This updates to the comment so that it's correctly picked up as deprecated.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

reference/reference.go

@@ -177,7 +177,8 @@ func splitDomain(name string) (string, string) {
 // hostname and name string. If no valid hostname is
 // found, the hostname is empty and the full value
 // is returned as name
-// DEPRECATED: Use Domain or Path
+//
+// Deprecated: Use [Domain] or [Path].
 func SplitHostname(named Named) (string, string) {
 	if r, ok := named.(namedRepository); ok {
 		return r.Domain(), r.Path()