The instructions for this driver, on the configuration page you linked, are very confusing. What they are saying is that you need to put the sub-options for the driver in an object on the safari.options
key, like so:
environments: [ {
browserName: 'safari',
version: 'ANY',
platform: 'MAC',
'safari.options': { dataDir: '/Users/[username]/Library/Safari' }
} ]