[operators] lifted variable out of loop

It doesn't change with each iteration, so it might as well be defined
outside of the loop.

Commit courtesy of Håkan Kjellerstrand.

src/operators.pod

@@ -21,9 +21,9 @@ horizontal bars:
     my $label-area-width = 1 + [max] @scores».key».chars;
     my $max-score        = [max] @scores».value;
     my $unit             = ($screen-width - $label-area-width) / $max-score;
+    my $format           = '%- ' ~ $label-area-width ~ "s%s\n";
 
     for @scores {
-        my $format = '%- ' ~ $label-area-width ~ "s%s\n";
         printf $format, .key, 'X' x ($unit * .value);
     }