Errors running example

[christopinka]

Example seems to be out of date with current Riker.

among other errors getting

 error[E0277]: the trait bound `Counter: Default` is not satisfied
   --> di-app/test/test.rs:63:32
    |
63  |     let actor = sys.actor_of::<Counter>("counter-1").unwrap();
    |                                ^^^^^^^ the trait `Default` is not implemented for `Counter`

[christopinka]

This seems to fix it

 #[actor(TestProbe, Add)]
#[derive(Default)]
struct Counter {
    probe: Option<TestProbe>,
    count: u32,
}