use cfg of spotify object

TODO:
- apply this to other single config values that are passed directly, e.g. in the
  statusbar
- use a more appropriate object to hold `cfg`

src/config.rs

@@ -19,7 +19,7 @@ pub struct Config {
     pub backend_device: Option<String>,
     pub volnorm: Option<bool>,
     pub volnorm_pregain: Option<f32>,
-    pub notify: Option<bool>
+    pub notify: Option<bool>,
 }
 
 #[derive(Serialize, Deserialize, Debug, Default, Clone)]