[jfx11u] RFR: 8307641: Change JavaFX release version to 11.0.20 in jfx11u

[Johan Vos]

Increase security version for JavaFX 11 to 20
Fix for JDK-8307641

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Commit messages:
 - Increase security version for JavaFX 11 to 20

Changes: https://git.openjdk.org/jfx11u/pull/139/files
 Webrev: https://webrevs.openjdk.org/?repo=jfx11u&pr=139&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8307641
  Stats: 2 lines in 2 files changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jfx11u/pull/139.diff
  Fetch: git fetch https://git.openjdk.org/jfx11u.git pull/139/head:pull/139

PR: https://git.openjdk.org/jfx11u/pull/139