Update to Swift 4.2

[quangctkm9207]

No description provided.

[ericdesa]

Thank you for your MR @quangctkm9207👍
I don't use Travis, but I think it failed because of the osx_image used here: https://github.com/Draveness/DKChainableAnimationKit/blob/master/.travis.yml#L2
The lib need to be compiled on xcode10 (https://docs.travis-ci.com/user/reference/osx)