Fix user management example

examples/user_management.rs

@@ -1,5 +1,6 @@
 use anyhow::*;
-use futures::{future::BoxFuture, FutureExt};
+use futures_core::future::BoxFuture;
+use futures_util::FutureExt;
 use log::LevelFilter;
 use northstar::{
     GEMINI_MIME,
@@ -51,7 +52,7 @@ fn handle_request(request: Request) -> BoxFuture<'static, Result<Response>> {
                 if request.path_segments()[0].eq("push") { // User connecting to /push
                     if let Some(push) = request.input() {
                         user.as_mut().push_str(push);
-                        user.save();
+                        user.save()?;
                     } else {
                         return Ok(Response::input_lossy("Enter a string to push"));
                     }