place backticks around FileManager.default

Author: jpsim

Foundation/NSFileManager.swift

@@ -70,7 +70,7 @@ public class FileManager: NSObject {
 
     /* Returns the default singleton instance.
     */
-    public static let default = FileManager()
+    public static let `default` = FileManager()
 
     /* Returns an NSArray of NSURLs locating the mounted volumes available on the computer. The property keys that can be requested are available in NSURL.
      */