Bug 1554059 [wpt PR 16991] - Update interfaces/webrtc.idl, a=testonly

Automatic update from web-platform-tests
Update interfaces/webrtc.idl (#16991)

Source: https://github.com/tidoust/reffy-reports/blob/0ff6a6d/whatwg/idl/webrtc.idl
Build: https://travis-ci.org/tidoust/reffy-reports/builds/536627667
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wp5At-commits: aed46771f380c18b28eb6544dcfe9b23165d9e67
wpt-pr: 16991

UltraBlame original commit: 8f58d6287e88d93ea4841f9ab2eb59b59c70c2e6

Author: marco-c

testing/web-platform/tests/interfaces/webrtc.idl

@@ -382,7 +382,7 @@ dictionary RTCRtpContributingSource {
     required DOMHighResTimeStamp timestamp;
     required unsigned long source;
              double audioLevel;
-             unsigned long rtpTimestamp;
+    required unsigned long rtpTimestamp;
 };
 
 dictionary RTCRtpSynchronizationSource : RTCRtpContributingSource {