Import (guix hash) in build-aux/download.scm.

* build-aux/download.scm: Import (guix hash).
  Reported by Matthew Lien <bluet@bluet.org>.

THANKS

@@ -9,6 +9,7 @@ suggestions, bug reports, patches, or general infrastructure help:
       Daniel Clark <dclark@pobox.com>
    Alexandru Cojocaru <xojoc@gmx.com>
        Aleix Conchillo Flaqué <aconchillo@gmail.com>
+     Matthew Lien <bluet@bluet.org>
         Alex Sassmannshausen <alex.sassmannshausen@gmail.com>
        Jason Self <jself@gnu.org>
         Alen Skondro <askondro@gmail.com>

build-aux/download.scm

@@ -25,7 +25,8 @@
              (web client)
              (rnrs io ports)
              (srfi srfi-11)
-             (guix utils))
+             (guix utils)
+             (guix hash))
 
 (define %url-base
   "http://alpha.gnu.org/gnu/guix/bootstrap"