Update example

Clear presence if input is empty.

examples/discord_presence/src/main.rs

@@ -34,8 +34,13 @@ fn main() {
         let mut buf = String::new();
 
         io::stdin().read_line(&mut buf).unwrap();
+        buf.pop();
 
-
+        if buf.is_empty() {
+            if let Err(why) = drpc.clear_activity() {
+                println!("Failed to clear presence: {}", why);
+            }
+        } else {
             if let Err(why) = drpc.set_activity(|a| a
                 .state(buf)
                 .assets(|ass| ass
@@ -46,5 +51,6 @@ fn main() {
             {
                 println!("Failed to set presence: {}", why);
             }
+        }
     };
 }