Merge pull request kodecocodes#536 from remlostime/binary-tree-swift

[Swift 4] Update Binary Tree

Author: kelvinlauKL

Binary Tree/BinaryTree.playground/Contents.swift

@@ -1,5 +1,10 @@
 //: Playground - noun: a place where people can play
 
+// last checked with Xcode 9.0b4
+#if swift(>=4.0)
+print("Hello, Swift 4!")
+#endif
+
 public indirect enum BinaryTree<T> {
   case node(BinaryTree<T>, T, BinaryTree<T>)
   case empty