chore: bump spring-boot-starter-parent to 2.3.4.RELEASE
chore: bump spring-boot-starter-parent to 2.3.4.RELEASE

So that the project can be started with OpenJDK 11 and newer versions.

Fixes https://github.com/darrachequesne/spring-data-jpa-datatables-sample/issues/12

darrachequesne/spring-data-jpa-datatables-sample,darrachequesne/spring-data-jpa-datatables-sample,darrachequesne/spring-data-jpa-datatables-sample