typo in variable name

Author: rocky

mathics/autoload/settings.m

@@ -15,4 +15,4 @@
 inside a notbook. *)
 System`$Notebooks::usage = "Set True if the Mathics is being used with a notebook-based front end.";
 System`$Notebooks = False;
-Unprotect[System`Notebooks];
+Unprotect[System`$Notebooks];