Specify minimal value for postgres scans

(cherry picked from commit 6a6d589)

Author: AMDmi3

plugins/node.d/postgres_scans_.in

@@ -73,6 +73,7 @@ my $pg = Munin::Plugin::Pgsql->new(
         "SELECT datname FROM pg_database WHERE datallowconn AND NOT datistemplate AND NOT datname='postgres' ORDER BY 1 LIMIT 10",
     stack     => 1,
     graphtype => 'DERIVE',
+    graphmin  => 0
 );
 
 $pg->Process();