RFR: 8288450: Update attribution in gstreamer.md file

[Alexander Matveev]

Doc-only change to update the license attribution in our gstreamer.md and glib.md files.

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

Changes: https://git.openjdk.org/jfx/pull/807/files
 Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=807&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8288450
  Stats: 128 lines in 2 files changed: 126 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jfx/pull/807.diff
  Fetch: git fetch https://git.openjdk.org/jfx pull/807/head:pull/807

PR: https://git.openjdk.org/jfx/pull/807