Make js-beautify dependency optional

[proppy]

It would be nice if the dependencies on js-beautify was optional as it brings quite a few transitive dependencies:

├─┬ [email protected]
│ ├─┬ [email protected]
│ │ ├── [email protected]
│ │ └── [email protected]
│ ├─┬ [email protected]
│ │ ├── [email protected]
│ │ ├─┬ [email protected]
│ │ │ ├── [email protected]
│ │ │ └── [email protected]
│ │ ├── [email protected]
│ │ └── [email protected]
│ ├── [email protected] deduped
│ ├── [email protected]
│ └─┬ [email protected]
│   └── [email protected]

and it's not strictly required for producing valid ES module output.