change listen_host for fast2 variant

Author: eserte

bin/setup-cpantestersmatrix-doit.pl

@@ -29,7 +29,7 @@
 EOF
 	unit_name          => 'cpan-testers-matrix', # used also for description and pidfile name # in this caseshould be cpan-testers-matrix.fast2
 	port               => 5002,
-        listen_host        => '',
+        listen_host        => '127.0.0.1',
 	external_url       => 'https://fast2-matrix.cpantesters.org', # used for ping test
     },
     fast => {