Merge pull request #1777 from ahoppen/access-level-import-guarded

Guard access-level import by `compiler(>=6)`

Author: ahoppen

Sources/SwiftExtensions/FileManagerExtensions.swift

@@ -10,7 +10,11 @@
 //
 //===----------------------------------------------------------------------===//
 
+#if compiler(>=6)
 package import Foundation
+#else
+import Foundation
+#endif
 
 extension FileManager {
   /// Same as `fileExists(atPath:)` but takes a `URL` instead of a `String`.