D3.js change diagonal line style

I am new to working with d3.js

I'm trying to change the style of the links in the interactive tree example that comes bundled with d3.js https://github.com/mbostock/d3/blob/master/examples/tree/tree-interactive.html

they are currently beziers and I would like them to be angular, that is, diagram style connections of the visio class.

it seems like there must be some additional definition of the diagonal around lines 42-43, but I can't tell from the documentation what that would be.

any help is most appreciated.