text not centered

HTML

<script src="https://rawgithub.com/kangax/fabric.js/master/dist/fabric.js"></script>
<canvas id="c" width="600" height="600"></canvas>

CSS

canvas {
    border: 1px solid #ccc;
}

JavaScript

var canvas = new fabric.Canvas('c', { selection: false });
var text = new fabric.Text('hello world', {
  fontSize: 30
});

var circle = new fabric.Circle({
  radius: 100,
  fill: '#eef',
});

var group = new fabric.Group([ circle, text ], {
  left: 150,
  top: 100,
  angle: -10
});

canvas.add(group);