Update compiler version check for custom file extensions

Sources/Zip/Zip.swift

@@ -12,7 +12,7 @@ import Foundation
 /// Main class that handles zipping and unzipping of files.
 public class Zip {
     // Set of vaild file extensions
-    #if compiler(>=6.0)
+    #if compiler(>=5.10)
         nonisolated(unsafe) private static var customFileExtensions: Set<String> = []
     #else
         private static var customFileExtensions: Set<String> = []