Change driver in start_session

[ImmortalDragonm]

In confix.mix I set default driver to phantomjs
config :hound, driver: "phantomjs"
but in some tests I want to use chrome_driver.
How to do it?
start_session %{browser: "chrome_driver"}
don't work, it's for browser only, not for driver
start_session %{driver: %{browserName: "chrome_driver"}}
don't work too.