iOS tutorials contain error

[alexvbush]

Original issue: uber/RIBs#210

I use ios/tutorials/tutorial1 and follow every steps in wiki/iOS-Tutorial-1 and wiki/iOS-Tutorial-2. The project doesn't compile once tutorial 2 is finished. I don't have much experience in Swift and it's a bit painful to pin down the cause, nor do I have enough experience see if I did anything wrong in RIB architecture. I mean, I'm interested in the architecture, and I want to follow the tutorials and see how it works. The sample code should just compile if I follow every single step in the tutorial. Please correct the sample code or steps in tutorials. Thank you.