RFR: 8254101: Update copyright header for files modified in 2020

Tue Dec 22 08:18:07 UTC 2020

Fix for updating last modified year in the files that were modified during year 2020.
@kevinrushforth, Please take a look.

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Commit messages:
 - update-copyright-2020

Changes: https://git.openjdk.java.net/jfx/pull/370/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jfx&pr=370&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8254101
  Stats: 196 lines in 196 files changed: 0 ins; 0 del; 196 mod
  Patch: https://git.openjdk.java.net/jfx/pull/370.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/370/head:pull/370

PR: https://git.openjdk.java.net/jfx/pull/370