Update example in doc of Sftp::subsystem

Signed-off-by: Jiahao XU <[email protected]>

Author: NobodyXu

src/session.rs

@@ -225,7 +225,7 @@ impl Session {
     /// # async fn main() -> Result<(), Box<dyn Error>> {
     ///
     /// use openssh::{Session, KnownHosts, Stdio};
-    /// use openssh_sftp_client::highlevel::Sftp;
+    /// use openssh_sftp_client::Sftp;
     ///
     /// let session = Session::connect_mux("[email protected]", KnownHosts::Strict).await?;
     ///