Update for swift 4

[christoff-1992]

As a result of updating the pod 'DataSource' the minimum target is now 9.0, however since we are now on iOS 11.x hopefully this shouldnt be an issue. 🤞

[christoff-1992]

@flipacholas - I see the build has failed, however travis is targeting "osx_image": "xcode8", but due to updating 'DATASource' to 7.0.2 the minimum deployment target has been uplifted to iOS 9.0. Is this something that you would be happy with now that we are on iOS 11.X?

Also can I ask why are you returning the mainQueue for the test target?

private static func backgroundConcurrencyType() -> NSManagedObjectContextConcurrencyType {
        return TestCheck.isTesting ? .mainQueueConcurrencyType : .privateQueueConcurrencyType
    }

I have some of my own tests in my local project and this will return the wrong context, I can change this locally but is there any advantage if we require the privateQueue.

[flipacholas]

Thanks for your support! I'll try to review later next week since I'm tied up most of this one.

[flipacholas]

The version number is meant to be in sync with DataStack. I guess it could be changed to 7.0.3.1 to avoid any overlap.

[christoff-1992]

Entirely up to yourself :) @flipacholas - Thanks for taking a look I will leave the pull request for you to either close or accept after amending to suit your needs.

[flipacholas]

I normally bring the project forward pulling the changes from DataStack, but since this is just meant to bring Swift 4 support I could merge it as well.