Update module pion/webrtc/v3 to v3.0.0-beta.4

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change
github.com/pion/webrtc/v3	require	patch	v3.0.0-20200701031423-a1bbddd0d86f -> v3.0.0-beta.4

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Release Notes

pion/webrtc

### [`v3.0.0-beta.4`](https://togithub.com/pion/webrtc/compare/v3.0.0-beta.3...v3.0.0-beta.4) [Compare Source](https://togithub.com/pion/webrtc/compare/v3.0.0-beta.3...v3.0.0-beta.4) ### [`v3.0.0-beta.3`](https://togithub.com/pion/webrtc/compare/v3.0.0-beta.2...v3.0.0-beta.3) [Compare Source](https://togithub.com/pion/webrtc/compare/v3.0.0-beta.2...v3.0.0-beta.3) ### [`v3.0.0-beta.2`](https://togithub.com/pion/webrtc/compare/v3.0.0-beta.1...v3.0.0-beta.2) [Compare Source](https://togithub.com/pion/webrtc/compare/v3.0.0-beta.1...v3.0.0-beta.2)

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