How do you remove the background gridlines in nvd3.js?-open source projects novus/nvd3

I am making a bar graph in nvd3.js, similar to this example: http://nvd3.org/ghpages/discreteBar.html. I was wondering if there was a way to remove the gridline so the background would be plain white. All of the examples use gridlines. I also checked the source code and didn’t see anything in the discreteBar model that would make this possible.