gnu: ocamlcudf: Fix reference to output.

* gnu/packages/ocaml.scm
  (ocamlcudf)[arguments]<#:make-flags>: Use #$output.

Signed-off-by: Mathieu Othacehe <othacehe@gnu.org>

gnu/packages/ocaml.scm

@@ -583,10 +583,9 @@ (define-public ocaml-cudf
         ("ocaml-ounit" ,ocaml-ounit)))
     (arguments
      `(#:make-flags
-       (list
-         "all" "opt"
-         (string-append "BINDIR=" (assoc-ref %outputs "out")
-                        "/bin"))
+       ,#~(list
+           "all" "opt"
+           (string-append "BINDIR=" #$output "/bin"))
        #:phases
        (modify-phases %standard-phases
          (delete 'configure))))