fix: stereo sound support for Chrome & Safari

[Previsou]

Description

Regex matching was incorrect, and 'stereo=1' was not munged into the SDP. Tested under Chrome, Firefox & Safari

Type of change

• [x] Bug fix (non-breaking change which fixes an issue)

Checklist

• [x] I've read & comply with the contributing guidelines
• [x] I have tested my code for new features & regressions on both mobile & desktop devices, using the latest version of major browsers.
• [x] I have made corresponding changes to the documentation (README.md).
• [x] I've checked my modifications for any breaking changes.