Update snippet to use fileURL instead of URL

I was having issues with this returning nil, changing the method to fileURLWithPath fixed it.

documents.m

@@ -4,4 +4,4 @@
 // Language: Objective-C
 // Completion Scope: Function or Method
 
-NSURL *documentsDirectoryURL = [NSURL URLWithString:[NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) firstObject]];
+NSURL *documentsDirectoryURL = [NSURL fileURLWithPath:[NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) firstObject]];