def square_crop(gravity = 'Center')
      gravity(gravity) unless gravity.nil?
      d = [width, height].min
      crop("#{d}x#{d}+0+0!")
    end
def square_crop(gravity = 'Center')
      gravity(gravity) unless gravity.nil?
      d = [width, height].min
      crop("#{d}x#{d}+0+0!")
    end
Crop to a square, using the specified gravity.