You're using Prawn's old table API. Please check out Prawn's manual
and/or the source code to learn about the new API:
http://prawn.majesticseacreature.com/manual.pdf
https://github.com/sandal/prawn/blob/master/lib/prawn/table.rb
https://github.com/sandal/prawn/blob/master/lib/prawn/table/cell.rb
In short: You'll need to move the headers in as the first row of your
data array and pass :headers => true instead, and :border_width is now
a cell style, so you can at the least pass :cell_style =>
{:border_width => 0}. See the manual and the code for more details.
-be