gnu: cook: Update phase style.

* gnu/packages/cook.scm (cook)[arguments]: Use MODIFY-PHASES syntax and
end phase with #t.

gnu/packages/cook.scm

@@ -1,5 +1,6 @@
 ;;; GNU Guix --- Functional package management for GNU
 ;;; Copyright © 2014 John Darrington <jmd@gnu.org>
+;;; Copyright © 2018 Tobias Geerinckx-Rice <me@tobias.gr>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -41,8 +42,8 @@
     (arguments
      `(#:parallel-build? #f ; There are some nasty racy rules in the Makefile.
        #:phases
-       (alist-cons-before
-        'configure 'pre-conf
+       (modify-phases %standard-phases
+         (add-before 'configure 'pre-conf
            (lambda _
              (substitute* (append '("common/env.c")
                                   (find-files "test" "\\.sh"))
@@ -59,8 +60,8 @@
              (substitute* "test/00/t0077a.sh"
                (("ar qc") "ar qcU"))
 
-          (setenv "SH" (which "sh")))
-        %standard-phases)))
+             (setenv "SH" (which "sh"))
+             #t)))))
     (native-inputs `(("bison" ,bison)
                      ;; For building the documentation:
                      ("groff" ,groff)