leafer-ui 文档错误修复

[a-boom]

传入 canvasId 会报错，如下图：

实测传入 canvas 实例，可以正常 init

const query = wx.createSelectorQuery();
        query.select("#leafer").fields({
            size: true,
            node: true
        }).exec(res => {
            const canvas = res[0].node
            const leafer = new Leafer({
                view: canvas,
                eventer: this
            })
    
            const rect = new Rect({
                x: 100,
                y: 100,
                width: 100,
                height: 100,
                fill: '#32cd79',
                draggable: true,
            })
    
            leafer.add(rect)
        })

[leaferjs]

收到，感谢反馈～

[leaferjs]

问题已修复～