Update dependencies to beta.7.

This fixes corruption of the first keyframe of every stream.

go.mod

@@ -7,5 +7,5 @@ require (
 	github.com/gorilla/websocket v1.4.2
 	github.com/pion/rtcp v1.2.4
 	github.com/pion/rtp v1.6.1
-	github.com/pion/webrtc/v3 v3.0.0-beta.6
+	github.com/pion/webrtc/v3 v3.0.0-beta.7
 )

go.sum

@@ -144,8 +144,8 @@ github.com/pion/turn/v2 v2.0.4 h1:oDguhEv2L/4rxwbL9clGLgtzQPjtuZwCdoM7Te8vQVk=
 github.com/pion/turn/v2 v2.0.4/go.mod h1:1812p4DcGVbYVBTiraUmP50XoKye++AMkbfp+N27mog=
 github.com/pion/udp v0.1.0 h1:uGxQsNyrqG3GLINv36Ff60covYmfrLoxzwnCsIYspXI=
 github.com/pion/udp v0.1.0/go.mod h1:BPELIjbwE9PRbd/zxI/KYBnbo7B6+oA6YuEaNE8lths=
-github.com/pion/webrtc/v3 v3.0.0-beta.6 h1:clI3mrXyk0ZC5WmdDLEQZOJbvqdk2za5l3mAm7WAVeQ=
-github.com/pion/webrtc/v3 v3.0.0-beta.6/go.mod h1:g2FHuaaKKuoZ9RlKIDAYvnO/rhocYG/d+2Ly1hRa85o=
+github.com/pion/webrtc/v3 v3.0.0-beta.7 h1:wDzex7YkT3wErRGaW4yOs9ziCQeuVF04poWVTqQ8o/Q=
+github.com/pion/webrtc/v3 v3.0.0-beta.7/go.mod h1:g2FHuaaKKuoZ9RlKIDAYvnO/rhocYG/d+2Ly1hRa85o=
 github.com/pkg/errors v0.8.1/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=
 github.com/pkg/errors v0.9.1 h1:FEBLx1zS214owpjy7qsBeixbURkuhQAwrK5UwLGTwt4=
 github.com/pkg/errors v0.9.1/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=