chore(build): Support Java 15

[workeitel]

Java 14 is out of date and new new latest version is 15 according to
https://en.wikipedia.org/wiki/Java_version_history

Keeping Java14 for backwards compatibility since 15 is very new.

example:

$ java -version
openjdk version "15.0.1" 2020-10-20
OpenJDK Runtime Environment Corretto-15.0.1.9.1 (build 15.0.1+9)
OpenJDK 64-Bit Server VM Corretto-15.0.1.9.1 (build 15.0.1+9, mixed mode, sharing)

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By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license

[gitpod-io]

[mergify]

Thank you for contributing! Your pull request will be updated from master and then merged automatically (do not update manually, and be sure to allow changes to be pushed to your fork).

[aws-cdk-automation]

AWS CodeBuild CI Report

• CodeBuild project: AutoBuildProject6AEA49D1-qxepHUsryhcu
• Commit ID: c29504e
• Result: SUCCEEDED
• Build Logs (available for 30 days)

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[mergify]

Thank you for contributing! Your pull request will be updated from master and then merged automatically (do not update manually, and be sure to allow changes to be pushed to your fork).