def pngcrush(image)
      if SUPPORTS_PNGCRUSH && config[:pngcrush]
        crushed = "#{image}.crushed"
        system('pngcrush', '-q', '-rem alla', '-reduce', '-brute', image, crushed)
        FileUtils.mv(crushed, image)
      end
    end
def pngcrush(image)
      if SUPPORTS_PNGCRUSH && config[:pngcrush]
        crushed = "#{image}.crushed"
        system('pngcrush', '-q', '-rem alla', '-reduce', '-brute', image, crushed)
        FileUtils.mv(crushed, image)
      end
    end
rescue on environments without `which` (windows)