Buster exit code is 0 when tests fail

buster.js

var buster = require('buster');
var config = module.exports;
config['node tests'] = {
    environment: 'node',
    tests: [ 'fail.js' ]
};

fail.js

var buster = require('buster');
var assert = buster.assertions.assert;

buster.testCase('foo', {
    'bar': function() {
        assert.isTrue(false);
    }
});