ox-latex: Fix `listings' language for `latex' code blocks

* ox-latex.el (org-latex-listings-langs): Update custom variable.

lisp/ox-latex.el

@@ -651,7 +651,7 @@ passed to pdflatex."
     (fortran "fortran")
     (perl "Perl") (cperl "Perl") (python "Python") (ruby "Ruby")
     (html "HTML") (xml "XML")
-    (tex "TeX") (latex "TeX")
+    (tex "TeX") (latex "[LaTeX]TeX")
     (shell-script "bash")
     (gnuplot "Gnuplot")
     (ocaml "Caml") (caml "Caml")