org-manual: Fix typo

* doc/org-manual.org (Hard indentation): Fix typo.

doc/org-manual.org

@@ -18533,7 +18533,7 @@ line up with the outline headers.  You would use these settings:
 
   #+vindex: org-odd-levels-only
   The third setting makes Org use only odd levels, 1, 3, 5, ..., in
-  the outline to create more indentation.  On a  per-file level,
+  the outline to create more indentation.  On a per-file level,
   control this with:
 
   #+begin_example