ox-texinfo: Fix language case

* lisp/ox-texinfo.el (org-texinfo-template): Fix language and encoding
  case.

Thanks to Brian J. Carlson for reporting it and providing a patch.
http://permalink.gmane.org/gmane.emacs.orgmode/89965

lisp/ox-texinfo.el

@@ -541,8 +541,7 @@ holding export options."
 	 "^@documentencoding \\(AUTO\\)$"
 	 coding
 	 (replace-regexp-in-string
-	  "^@documentlanguage \\(AUTO\\)$" language header nil nil 1)
-	 nil nil 1)))
+	  "^@documentlanguage \\(AUTO\\)$" language header t nil 1) t nil 1)))
      ;; Additional header options set by #+TEXINFO_HEADER.
      (let ((texinfo-header (plist-get info :texinfo-header)))
        (and texinfo-header (org-element-normalize-string texinfo-header)))