ox-latex: Use "french" instead of "frenchb" Babel language

* lisp/ox-latex.el (org-latex-babel-language-alist): Use "french"
  instead of obsolete "frenchb".

lisp/ox-latex.el

@@ -179,7 +179,7 @@
     ("et" . "estonian")
     ("eu" . "basque")
     ("fi" . "finnish")
-    ("fr" . "frenchb")
+    ("fr" . "french")
     ("fr-ca" . "canadien")
     ("gl" . "galician")
     ("hr" . "croatian")