Make the connection references weak references.

lib/AnyEvent/NSQ/Reader.pm

@@ -7,6 +7,7 @@ package AnyEvent::NSQ::Reader;
 use strict;
 use warnings;
 use Carp 'croak';
+use Scalar::Util qw( weaken );
 
 use parent 'AnyEvent::NSQ::Client';
 
@@ -58,6 +59,7 @@ sub _identified {
       ## Keep the connection in the registry in case the user
       ##  wants to issue FIN/REQs inside the callback
       $self->{routing}->{$msg->{message_id}} = $conn;
+      weaken( $self->{routing}->{$msg->{message_id}} );
 
       my $action = $self->{message_cb}->($self, $msg);