Update to Swift 4.2 and iOS 12

[LambdaDigamma]

Carthage Build for iOS 12 project fails with exit code 65. This usually indicates that project itself failed to compile.

./ContextMenu/ContextMenuPresentationController.swift:56:30: error: value of type 'CGRect' has no member 'dominantCorner'

[yonlau]

I encounter same issue, please help to update for that, thanks!

[manuelsalinas-legion]

Hello @rnystrom Will you give support for iOS 12 and swift 4.2?

[yonlau]

Use the latest version and build the code, drag the ContextMenu into to project manually solve my problem!

[rnystrom]

Merged #37 for 4.2 support. I don't use Carthage, so not sure what's going on there.

FYI this project is open source, don't have to wait on me for a fix 😉

[sbarow]

#41 should fix Swift 4.2 support for Carthage checkouts.