Use Math.round() instead of Math.ceil() to match AngularJS.

The front end (using AngularJS) rounds percents up; whereas the embedded widget using api always rounds down.

Compare https://www.bountysource.com/fundraisers/475-lzma-js (17%) with https://api.bountysource.com/user/fundraisers/475/embed (16%).

This pull requests makes the api round percents to match the front end.