MT#18395 widget sorting fix

interestingly, the sorting with a malformed comparison used here

sort {$a > $b} @elements

gives different results on master (mr4.2x) and mr3.8.5. however,
results are the same with correct comparison.

sort {$a <=> $b} @elements

Change-Id: I62f0fd65b62a1db24ee9e2cc735839e30d5da916

lib/NGCP/Panel/Widget.pm

@@ -25,7 +25,7 @@ sub instantiate_plugins {
             push @instances, { instance => $inst, name => $_ };
         }
     }
-    return sort {$a->{instance}->priority > $b->{instance}->priority} @instances;
+    return sort {$a->{instance}->priority <=> $b->{instance}->priority} @instances;
 }
 
 no Moose;