Release v2.4.0 (#386)
Release v2.4.0 (#386)

* [Gradle Release Plugin] - pre tag commit:  'v2.4.0'.

* [Gradle Release Plugin] - new version commit:  'v2.4.1-SNAPSHOT'.
GoogleCloudPlatform/app-gradle-plugin,GoogleCloudPlatform/app-gradle-plugin,GoogleCloudPlatform/app-gradle-plugin