RFR: build: update to Gradle 6.3

[Robin Westberg]

On Wed, 29 Apr 2020 07:41:07 GMT, Erik Helin <ehelin at openjdk.org> wrote:

> Hi all,
> 
> please review this patch that updates Gradle to version 6.3.
> 
> Testing:
> - `sh gradlew images`
> - `sh gradlew test`
> 
> Thanks,
> Erik

Looks good!

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Marked as reviewed by rwestberg (Reviewer).

PR: https://git.openjdk.java.net/skara/pull/614