egg index.d.ts 定义遗漏属性
## What happens?
A clear and concise description of what the bug is.
egg-development 中 config 可以  配置  overrideIgnore: boolean;
但是egg index.d.ts 中缺少此属性的定义，希望可以补上


![image](https://user-images.githubusercontent.com/7607540/94901764-b49c1e80-04c9-11eb-91dc-d4a6d3a367eb.png)

## Mini Showcase Repository(REQUIRED)
> Provide a mini GitHub repository which can reproduce the issue.
> Use `npm init egg --type=simple bug` then upload to your GitHub

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## How To Reproduce

**Steps to reproduce the behavior:**
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**Expected behavior**
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## Context
- **Node Version**:
- **Egg Version**:
- **Plugin Name**:
- **Plugin Version**:
- **Platform**:
