Freeze string literal

Author: mrkn

lib/unicode_plot/block_canvas.rb

@@ -24,10 +24,10 @@ def initialize(width, height, fill_char=0, **kw)
     ].freeze
 
     BLOCK_DECODE = [
-      ' ', '▗', '▖', '▄',
-      '▝', '▐', '▞', '▟',
-      '▘', '▚', '▌', '▙',
-      '▀', '▜', '▛', '█'
+      -' ', -'▗', -'▖', -'▄',
+      -'▝', -'▐', -'▞', -'▟',
+      -'▘', -'▚', -'▌', -'▙',
+      -'▀', -'▜', -'▛', -'█'
     ].freeze
 
     def lookup_encode(x,y) ; BLOCK_SIGNS[x][y] ; end