Use tokio for hello_world example

The crate tokio-core is deprecated.

Cargo.toml

@@ -32,7 +32,7 @@ version = "0.2.2"
 
 [dev-dependencies]
 ruma-events = "0.11.0"
-tokio-core = "0.1.17"
+tokio = "0.1"
 
 [features]
 default = ["tls"]

examples/hello_world.rs

@@ -9,7 +9,6 @@ use ruma_events::{
     EventType,
 };
 use ruma_identifiers::RoomAliasId;
-use tokio_core::reactor::Core;
 use url::Url;
 
 // from https://stackoverflow.com/a/43992218/1592377
@@ -66,8 +65,6 @@ fn main() {
         }
     };
 
-    Core::new()
-        .unwrap()
-        .run(hello_world(homeserver_url.parse().unwrap(), room))
-        .unwrap();
+    tokio::run(hello_world(homeserver_url.parse().unwrap(), room)
+               .map_err(|e| { dbg!(e); () }));
 }