HMR not working on wsl2.
## What happens?
HMR not working on wsl2. Does egg-bin has workaround like 'poll' for webpack?

## 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

<!-- https://github.com/YOUR_REPOSITORY_URL -->

## How To Reproduce

**Steps to reproduce the behavior:**
1. run any egg project on wsl2
2. make some change, hmr not working.

**Expected behavior**
1. hmr working.
2.

## Context
- **Node Version**: v14.5.0
- **Egg Version**:  2.14.0
- **Plugin Name**:
- **Plugin Version**:
- **Platform**: wsl2 
