Make gradle script compatible with 6.0

[tobiasdiez]

Currently, gradle reports

Deprecated Gradle features were used in this build, making it incompatible with Gradle 6.0.
Use '--warning-mode all' to show the individual deprecation warnings.
See https://docs.gradle.org/5.6/userguide/command_line_interface.html#sec:command_line_warnings

As we want to upgrade to Gradle 6 at some point, these deprecated features should be migrated.

[vpbhargav]

I would like to work on this. Can you assign it to me please?

[matthiasgeiger]

Thanks for your interest! Just go ahead!

[koppor]

This is for Gradle 7.0, because we updated to Gradle 6.0 and everything works, right?

[tobiasdiez]

It was for Gradle 6.