Upgradle to 5.6
Upgradle to 5.6

Here are the highlights of this release:
 - Incremental Groovy compilation
 - Groovy compile avoidance
 - Test fixtures for Java projects
 - Manage plugin versions via settings script

For more details see https://docs.gradle.org/5.6/release-notes.html

junit-team/junit-lambda,sbrannen/junit-lambda