Carthage update/bootstrap download Swift 3.1 RealmSwift module for swift 4

[liuxuan30]

I met a strange issue that even though I updated realm or fresh install 2.10.2, Xcode9 still complains the module is compiled with swift 3.1.

I opened one here: realm/realm-swift#5384

[pmairoldi]

Ya you can't use the downloaded one you have to build from source for swift 4. I ran into the same issue.

[liuxuan30]

I updated carthage then, it will pick the right framework finally, my carthage is too old