Update the version of lint-staged (#14971)

## Description
Fix #14784 

## How has this been tested?
1. `git add modified-files`, call the files VersionA
2. `git commit -m "some messages"`, then the program will run `npm run -s precommit` to check lint styles and some other things.
3. Encounter some errors like "Multiple spaces found", so you change the code again and save, call the files VersionB. But do not `git add` again.
4. `git commit` again, failed. Because now the `lint-staged` only check staged changes (i.e, VersionA).
You should `git add` again and then `git commit`

## Screenshots <!-- if applicable -->
The screenshot of running `git commit` with old version of `lint-staged`
![image](https://user-images.githubusercontent.com/24849874/56072453-06486a80-5d65-11e9-990a-9447b14abd9a.png)
The screenshot of running `git commit` with latest version of `lint-staged`. The blue boxes highlight the difference
![image](https://user-images.githubusercontent.com/24849874/56072493-84a50c80-5d65-11e9-8373-77353c8601ac.png)


## Types of changes
Upgrade lint-staged

## Checklist:
- [X] My code is tested.
- [X] My code follows the WordPress code style. <!-- Check code: `npm run lint`, Guidelines: https://make.wordpress.org/core/handbook/best-practices/coding-standards/javascript/ -->
- [X] My code follows the accessibility standards. <!-- Guidelines: https://make.wordpress.org/core/handbook/best-practices/coding-standards/accessibility-coding-standards/ -->
- [X] My code has proper inline documentation. <!-- Guidelines: https://make.wordpress.org/core/handbook/best-practices/inline-documentation-standards/javascript/ -->
- [X] I've included developer documentation if appropriate. <!-- Handbook: https://wordpress.org/gutenberg/handbook/designers-developers/ -->