Update Gradle version

[serhii-lekariev]

Current version of Gradle wrapper used in Spine is 4.10.2.

Bumping it to the most recent 5.1 version would, among other things, update Gradle's own dependencies so that the versions don't clash.

Currently, the version clash does not allow to redirect logging in the model-verifier module, since it explicitly depends on gradleApi() and transitively depends on org.slf4j:slf4j-api:1.7.25.slf4j.
As gradle-api.4.10.2.jar that exists as a result of depending on gradleApi() depends on an old version of SLF4J, a clash happens (namely, between two versions of the org.slf4j.event.EventRecodingLogger), resulting in obscure exceptions at runtime.