fix(datasets): restore eprintln for "Dataset updated" status line

Reverts fb8af95. The suggestion changed eprintln! to println!, which
puts the human prelude on stdout and breaks `-o json` / `-o yaml`
piping (e.g. `... -o json | jq` fails with a parse error because the
status line precedes the JSON).

Author: zfarrell

src/datasets.rs

@@ -524,7 +524,7 @@ pub fn update(
     let d: UpdateResponse = api.put(&format!("/datasets/{dataset_id}"), &body);
 
     use crossterm::style::Stylize;
-    println!("{}", "Dataset updated".green());
+    eprintln!("{}", "Dataset updated".green());
     match format {
         "json" => println!("{}", serde_json::to_string_pretty(&d).unwrap()),
         "yaml" => print!("{}", serde_yaml::to_string(&d).unwrap()),