Support renamed Chrome.app on macOS

[finngaida]

I got an error when launching helium via driver = start_chrome():

selenium.common.exceptions.WebDriverException: Message: unknown error: cannot find Chrome binary

After some trial and error I noticed Chrome gets installed into /Applications/Google Chrome.app by default, however I had renamed it to just Chrome.app, presumably breaking the binary lookup functionality of helium.
It was easily fixed by linking Chrome to the expexted path via ln -s /Applications/Chrome.app /Applications/Google\ Chrome.app -however an API access à la driver = start_chrome(binary_path="/Applications/Chome.app") would be preferable.