Tweak example output style

Author: stoned

doc/Type/Promise.pod6

@@ -220,8 +220,8 @@ creates a chained promise.
 
     my $timer = Promise.in(2);
     my $after = $timer.then({ say "2 seconds are over!"; 'result' });
-    say $after.result;  # 2 seconds are over
-                        # result
+    say $after.result;
+    # OUTPUT: «2 seconds are over␤result␤»
 
 =head2 method keep