To avoid installation failure like this:

```bash
npm ERR! Found: jest@27.0.1
npm ERR! node_modules/jest
npm ERR! dev jest@"^27.0.1" from the root project
npm ERR!
npm ERR! Could not resolve dependency:
npm ERR! peer jest@"^24.0.0 || ^25.0.0 || ^26.0.0" from jest-mock-extended@1.0.15
npm ERR! node_modules/jest-mock-extended
npm ERR! dev jest-mock-extended@"^1.0.13" from the root project
npm ERR!
npm ERR! Fix the upstream dependency conflict, or retry
npm ERR! this command with --force, or --legacy-peer-deps
npm ERR! to accept an incorrect (and potentially broken) dependency resolution.
```

• Commit 10e5e47
• #65: Add jest 27.0.0 as peer dependencies
• Branch master

Hantsy Bai