line.rb modified. You can do something like this:

g.data("1px", [25,36,86,39,25,31,79,88],nil,1) # line_width = 1px
g.data("3px", [22,29,35,38,36,40,46,57],nil,3) # line_width = 3px
g.data("10px", [90,34,23,12,78,89,98,88],nil,10) # line_width = 10px

If no width specificated, 5px width used as default.

test_line.rb also modified with examples.