[jfx11u] RFR: 8288450: Update attribution in gstreamer.md file

[Kevin Rushforth]

Clean backport.

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Commit messages:
 - 8288450: Update attribution in gstreamer.md file

Changes: https://git.openjdk.org/jfx11u/pull/111/files
 Webrev: https://webrevs.openjdk.org/?repo=jfx11u&pr=111&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8288450
  Stats: 6943 lines in 3 files changed: 293 ins; 6648 del; 2 mod
  Patch: https://git.openjdk.org/jfx11u/pull/111.diff
  Fetch: git fetch https://git.openjdk.org/jfx11u pull/111/head:pull/111

PR: https://git.openjdk.org/jfx11u/pull/111