As of now GreenHopper uses the new resolution called 'Done' which is defined in the list of system wide JIRA resolutions.
This is causing additional confusion to people using JIRA since there is already an existing 'Fixed' resolution. It should be configurable in GH to define which resolution should be used while using Simplified Workflow and it will used in the workflows while creating new projects using GreenHopper 'Getting Started' page.