org-bibtex.el (org-bibtex-no-export-tags): Fix docstring

* org-bibtex.el (org-bibtex-no-export-tags): Fix docstring.

Thanks to Leonard Randall for the fix.

lisp/org-bibtex.el

@@ -279,7 +279,7 @@ not be exported."
 
 (defcustom org-bibtex-no-export-tags nil
   "List of tag(s) that should not be converted to keywords.
-This variable is relevant only if `org-bibtex-export-tags-as-keywords' is t."
+This variable is relevant only if `org-bibtex-tags-are-keywords' is t."
   :group 'org-bibtex
   :version "24.1"
   :type '(repeat :tag "Tag" (string)))