ox.el (org-export-time-stamp-file): Fix docstring typo

* ox.el (org-export-time-stamp-file): Fix docstring typo.

lisp/ox.el

@@ -752,7 +752,7 @@ e.g. \"tasks:nil\"."
 
 (defcustom org-export-time-stamp-file t
   "Non-nil means insert a time stamp into the exported file.
-The time stamp shows when the file was created. This option can
+The time stamp shows when the file was created.  This option can
 also be set with the OPTIONS keyword, e.g. \"timestamp:nil\"."
   :group 'org-export-general
   :type 'boolean)