Default file type inconsistency

[Aziks0]

The README file states that the default file type is raw:

node-mic/README.md

Line 111 in 03f3d36

* `fileType`: Recording format. `raw` or `wav`. (default: `raw`)

But in the code, the default file type is wav:

node-mic/src/index.ts

Line 42 in 03f3d36

this._fileType = options.fileType || 'wav';

I didn't make a pull request, because I don't know which one you prefer to be set as the default.