Address clippy complaint about single match arm

I expect more arms to be added here later, but for the time being, let's
address the clippy complaint and swap this to an if let. It would be
nice if we could chain these ifs, it's not stabilized yet:
rust-lang/rust#53667

src/lib.rs

@@ -258,13 +258,10 @@ impl Simulation {
     /// An internal function used to wakeup sleeping Agents due to wake.
     fn wakeup_agents_scheduled_to_wakeup_now(&mut self) {
         for agent in self.agents.iter_mut() {
-            match agent.state {
-                AgentState::AsleepUntil(scheduled_wakeup) => {
-                    if self.time >= scheduled_wakeup {
-                        agent.state = AgentState::Active;
-                    }
+            if let AgentState::AsleepUntil(scheduled_wakeup) = agent.state {
+                if self.time >= scheduled_wakeup {
+                    agent.state = AgentState::Active;
                 }
-                _ => (),
             }
         }
     }