Specify minimum value for tuples

(cherry picked from commit b94dfbf)

Author: AMDmi3

plugins/node.d/postgres_tuples_.in

@@ -92,7 +92,7 @@ my $pg = Munin::Plugin::Pgsql->new(
     ],
     suggestquery =>
         "SELECT datname FROM pg_database WHERE datallowconn AND NOT datistemplate AND NOT datname='postgres' ORDER BY 1 LIMIT 10",
-    graphtype => 'DERIVE',
+    graphtype => 'DERIVE', graphmin => 0,
 );
 
 $pg->Process();