Migrated to Swift 4

Author: shabirjan

AVL Tree/AVLTree.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
+
 let tree = AVLTree<Int, String>()
 
 tree.insert(key: 5, payload: "five")