Summary:
Adds new ```space-evenly``` for ```justify-content```.
Also adds a typofix in one of the other justify-content tests.
Fixes#657
Closes https://github.com/facebook/yoga/pull/658
Differential Revision: D6407996
Pulled By: emilsjolander
fbshipit-source-id: cc837409e1345624b4bd72c31e25fe68dcb0f6a3