Explicitly flatten in Sierpinski triangle

Author: moritz

rosettacode/sierpinski_triangle.t

@@ -12,7 +12,7 @@ sub sierpinski ($n) {
     my @down  = '*';
     my $space = ' ';
     for ^$n {
-        @down = @down.map({"$space$_$space"}), @down.map({"$_ $_"});
+        @down = flat @down.map({"$space$_$space"}), @down.map({"$_ $_"});
         $space ~= $space;
     }
     return @down;