Actions.session() and Actions.sessions() issue

[afruth]

https://github.com/beatfactor/nightwatch/blob/master/lib/selenium/protocol.js

I believe that Actions.sessions() method should point to the /sessions endpoint instead of /session.

Also, the /session GET action should point to the /session/:sessionId endpoint, as it is now it throws an error.

As a suggestion maybe add the POST action in /session too (without sessionId) as per Selenium docs? https://code.google.com/p/selenium/wiki/JsonWireProtocol#/session

Keep up the good work 👍