Merge pull request #756 from artFintch/migration4.2/GCD

[Swift 4.2] Update GCD

Author: kelvinlauKL

GCD/GCD.playground/Contents.swift

@@ -1,10 +1,5 @@
 //: Playground - noun: a place where people can play
 
-// last checked with Xcode 9.0b4
-#if swift(>=4.0)
-print("Hello, Swift 4!")
-#endif
-
 // Recursive version
 func gcd(_ a: Int, _ b: Int) -> Int {
   let r = a % b