Add support for Yarn v2.x

[2hoyeong]

Describe the bug

Yarn berry no longer create node_modules. but apidoc find assets in node_modules

error: Could not find where dependencies of apidoc live!
error: The "path" argument must be of type string. Received undefined
[error] apidoc encountered an error during documentation generation!

Steps to reproduce

1. Create yarn berry project
2. Install apidoc >= 0.50
3. Build

Information

• Version of apidoc: ^0.50.2
• Operating system (e.g. GNU+Linux/MacOS/Windows): MacOS
• Node version: v16.4.1
• Browser (e.g. firefox, chrome):
• Yarn: 3.1.1

[NicolasCARPi]

Note to future self (or another contributor wanting to address this shortcoming): this should be used: https://yarnpkg.com/advanced/pnpapi/#accessing-the-files