[maven-release-plugin] copy for tag singleton-enforcer-2.1.0

[maven-release-plugin] copy for tag singleton-enforcer-2.0.1

[maven-release-plugin] copy for tag singleton-enforcer-2.0.0

[maven-release-plugin] copy for tag singleton-enforcer-1.0.1

[maven-release-plugin] copy for tag singleton-enforcer-1.0.0