旭日图的emphasis部分功能不工作

[billdagou]

• I am using English in this issue. 在这个 Issue 中我使用了英文（强烈建议）。

General Questions

• Required: I have read the document and examples and tried to solve it by myself. （必填）我读过了文档和教程，并且曾试图自己解决问题。
• Required: I have searched for similar issues and that didn't help. （必填）我搜索过 issue 但是没有帮助。
• Required: I have tried with the latest version of ECharts and still have this problem. （必填）我试过最新版本的 ECharts，还是存在这个问题。

In this issue, I have provided information with: 在这个 issue 中我提供了以下信息：

• Required: issue type；（必填）issue 类型
• Required: one sentence description in issue details；（必填）一句话的问题描述
• Required: demo；（必填）能反映问题的例子（如果你想提问或报 bug）
• Required: ECharts version；ECharts 版本

Issue Type

• I have a question to ask about how to use ECharts to ...；我想提问如何使用 ECharts 实现某功能
• I have a bug to report；我想要报 bug
• I have a feature to request, e.g.: I'd like a new feature that ...；我需要一个新功能
• I have a feature to enhance, e.g.: The current feature should be improved in the way that ...；我希望改进某个功能
• There's something wrong with the documents；文档有些问题
• Others, or I'm not sure which issue types to choose here；其他，或我不知道应该选什么类型

Issue Details

旭日图中，在鼠标hover状态下，series.label.emphasis.formatter无法覆写series.label.formatter

Expected Behavior

在鼠标hover状态下，series.label.emphasis能完美覆写series.label

Current Behavior

无任何反应

Online Example

http://gallery.echartsjs.com/editor.html?c=x6nJ3y31kx&v=1

option = { series: { type: 'sunburst', data: data, label: { formatter: '{c}', emphasis: { formatter: '{b}' } } } };

Topics

• Legend
• Tooltip
• Event
• Performance
• SVG
• Map
• ECharts GL
• Third-party libraries, e.g.: Vue.js, React

Anything Else We Need to Know

N/A

Environment

• ECharts version；ECharts 版本: 4.2.0-rc.2

• It happens only on certain browsers or operating systems. 对于特定浏览器或操作系统才会出现的问题，请提供相应环境信息：{BROWSER_VERSION_OR_OS_INFORMATION_HERE}