can't change border diagonal

[crgstar]

I tried to change cell border diagonal, but it doesn't work.

irb(main):001:0> require 'rubyXL/convenience_methods'
irb(main):002:0> workbook = RubyXL::Workbook.new
irb(main):003:0> worksheet = workbook[0]
irb(main):004:0> worksheet.add_cell(1, 1, 'B2')
irb(main):005:0> worksheet[1][1].change_border(:diagonal, 'thick')
irb(main):006:0> workbook.write("test.xlsx")

It seems like RubyXL has set the value of the border, but it is not visible.
I have noticed that changing other directions (top, bottom, left, right) works fine.
Could you please provide a solution or fix the bug?