Update Multiset to Swift 4.2

Author: BNTR

Multiset/Multiset.playground/Contents.swift

@@ -1,9 +1,5 @@
 //: Playground - noun: a place where people can play
 
-#if swift(>=4.0)
-  print("Hello, Swift 4!")
-#endif
-
 import Cocoa
 
 var set = Multiset<String>()