[Bug Report] v-chart 使用自定义渲染逻辑，报错Cannot read property 'getXScale' of undefined"

### VUX version
0.1.0

### OS/Browsers version
windows10/chrome64

### Vue version
2.5.16

### Code

```html

methods: {
renderVChart({ chart }) {
chart.source(this.data)
// 设置柱状图 横向
chart.coord({ transposed: true });
chart.render();
}
}

```

### Steps to reproduce
就是报错 Cannot read property 'getXScale' of undefined"

### What is Expected?
自定义渲染需要怎么操作。

### What is actually happening?
自定义渲染需要怎么操作。