Fix silly example

The mentions endpoint doesn't take a user_id, silly. It returns mentions
for the authorized user. Fix that.

Author: semifor

examples/api.pl

@@ -17,7 +17,7 @@
 my $r = $client->verify_credentials;
 say "$$r{screen_name} is authorized";
 
-my $mentions = $client->mentions({ user_id => $$r{id} });
+my $mentions = $client->mentions;
 for my $status ( @$mentions ) {
     say $$status{text};
 }