Incorrect MIME type for Opus files.

[scgehin]

Description

Opus files are given the MIME type "audio/opus", which is not correct. The problem originates from #53, which incorrectly references the RFC for RTP payloads.
The correct MIME type for Opus files is "audio/ogg; codecs=opus", as seen in sections 9 and 10 of this RFC defining the Opus file format.
This issue appears to be the root cause of thelounge/thelounge#4429.

Existing Issue Check

• I have searched the existing issues and could not find any related to my problem.

ESM (ECMAScript Module) Requirement Acknowledgment

• My project is an ESM project and my package.json contains the following entry: "type": "module".

File-Type Scope Acknowledgment

• I understand that file-type detects binary file types and not text or other formats.

[Borewit]

I agree @scgehin, do you want to create a PR to improve the MIME type mapping?