HashSet Code updated to Swift4

Author: shabirjan

Hash Set/HashSet.playground/Contents.swift

@@ -1,4 +1,8 @@
 //: Playground - noun: a place where people can play
+// last checked with Xcode 9.0b4
+#if swift(>=4.0)
+print("Hello, Swift 4!")
+#endif
 
 var set = HashSet<String>()