fixed value of `group` property for lock tasks

- `gradle tasks` will now print "Locking tasks" instead of "Locking tasks tasks"
Merge pull request #31 from pniederw/master

fixed value of `group` property for lock tasks
[Gradle Release Plugin] - new version commit:  '2.0.1'.
Use final version of plugin-plugin. Added -SNAPSHOT to version.
Merge branch 'master' into gradle-2.0.