Increase timeout for client_callbacks test (#229)

From 10ms to 50ms

Jack is too slow to load properties in 10ms.

The properties are loaded using  Berkeley DB, probably why

Author: worikgh

src/properties.rs

@@ -481,7 +481,7 @@ mod metadata {
 
         #[test]
         fn client_callbacks() {
-            let timeout = std::time::Duration::from_millis(10);
+            let timeout = std::time::Duration::from_millis(50);
             let prop1 = Property::new("foo", None);
             let prop2 = Property::new(
                 "http://churchofrobotron.com/2084",