Changed append to reflect convention property.
Changed append to reflect convention property.

GoogleCloudPlatform/gradle-appengine-plugin,mpoehler/gradle-appengine-plugin,ArseniKavalchuk/gradle-appengine-plugin,loosebazooka/gradle-appengine-plugin,MGronber/gradle-appengine-plugin,bmuschko/gradle-gae-plugin,judeebene/gradle-appengine-plugin