doc/org-manual.org (How to create a useful backtrace): Fix typo

* doc/org-manual.org (How to create a useful backtrace): Fix typo.

doc/org-manual.org

@@ -308,7 +308,7 @@ error occurred.  Here is how to produce a useful backtrace:
 
 2. Then, activate the debugger:
 
-   : M-x toggle-debug-or-error <RET>
+   : M-x toggle-debug-on-error <RET>
 
    #+texinfo: @noindent
    or, from the menu: Options \rarr Enter Debugger on Error.