Update Naive Bayes Classifier to Swift 4

Updated to Swift 4 and Xcode 9.0b4. No changes necessary.

Author: bobdel

Naive Bayes Classifier/NaiveBayes.playground/Contents.swift

@@ -1,5 +1,10 @@
 import Foundation
 
+// last checked with Xcode 9.0b4
+#if swift(>=4.0)
+print("Hello, Swift 4!")
+#endif
+
 /*:
  ## Naive Bayes Classifier