RFR: 7116: Update version to 8.1.0 in master [v5]

[Jie Kang]

On Mon, 25 Jan 2021 22:05:58 GMT, Marcus Hirt <hirt at openjdk.org> wrote:

>> Also cleaning up the maven versioning.
>
> Marcus Hirt has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Moving the plug-in xml

Marked as reviewed by jkang (Author).

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PR: https://git.openjdk.java.net/jmc/pull/206