We could also split the declaration of RawData with the "browser"
field:
```
// for Node.js
export type RawData = string | Buffer | ArrayBuffer | ArrayBufferView; // no Blob
// for the browser
export type RawData = string | ArrayBuffer | ArrayBufferView | Blob; // no Buffer
```
But it does not seem supported by the TypeScript compiler, so we'll
revert to just using "any" for now.
Related: https://github.com/socketio/engine.io-parser/issues/128
