Upgrade plugins-core to 0.8.1 (#364)
Upgrade plugins-core to 0.8.1 (#364)

Adds extended support for thin jar deployments, automatically copying
jars referenced in Class-Path in the source artifact to the staging
directory.
GoogleCloudPlatform/app-gradle-plugin,GoogleCloudPlatform/app-gradle-plugin,GoogleCloudPlatform/app-gradle-plugin