call wrap correctly

lib/RT/Extension/MergeUsers.pm

@@ -58,7 +58,7 @@ use RT::Interface::Web::Handler;
 use Hook::LexWrap;
 
 { my $i = 0;
-wrap 'RT::Interface::Web::Handler::CleanupRequest' => sub {
+wrap 'RT::Interface::Web::Handler::CleanupRequest', post => sub {
     return if ++$i%100; # flush cache every N requests
     %EFFECTIVE_ID_CACHE = ();
 }; }