Fix #4: Add workaround for missing focused property in outputs

If there is an inactive input, then the `focused` property may be missing in sway's response to a `get_output` message.
This fix uses a feature of serde where default values for missing fields can be defined.
Here, the `Default::default` for booleans is used, which is `false`.

src/main.rs

@@ -105,6 +105,7 @@ fn check_success(stream: &UnixStream) {
 #[derive(Serialize, Deserialize)]
 struct Output {
     name: String,
+    #[serde(default)]
     focused: bool,
     active: bool,
 }