v0.6.0

Assorted

• Add groupId to maven-clean-plugin (#17)
• Remove OBE Sonar properties (#20)
• Delete obsolete TravisCI config file (#22)

Dependency updates

• Bump mockito-core from 3.7.0 to 3.7.7 (#16)
• Update sonar-maven-plugin to 3.8.0.2131 (#18)