You have to call
BW::Location.start then you will be prompted to start allow of deny location permission.
Additionally, the permissions are managed in the simulator's Settings app, not in the Macs preference pane.
You might also have to set the messages to show in the permission popup in the Rakefile:
app.info_plist["NSLocationWhenInUseUsageDescription"] = "MyApp needs your location"
app.info_plist["NSLocationAlwaysUsageDescription"] = "MyApp needs your location"