Move warning text to stderr, where it belongs

oxo/cli.py

@@ -56,7 +56,8 @@ def shorten(urls: t.List[str] = typer.Argument(..., min=1), base_url=BASE_URL):
     if base_url == BASE_URL.default:
         typer.secho(
             f"Warning: shortening is often disabled "
-            f"for {BASE_URL.default}, command may fail",
+            f"for {base_url}, command may fail",
             fg=typer.colors.RED,
+            err=True,
         )
     typer.echo(api.shorten(base_url, urls))