RFR: 8254100: FX: Update copyright year in docs, readme files to 2021

[Jeanette Winzenburg]

On Thu, 22 Oct 2020 11:53:35 GMT, Kevin Rushforth <kcr at openjdk.org> wrote:

>> Copyright year in these 3 docs needs to be updated to 2021.
>
> Marked as reviewed by kcr (Lead).

just curious - why 2021? back to the future or do we already prepare for the next release?

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PR: https://git.openjdk.java.net/jfx/pull/330