artwork: Update to latest version.

* gnu/artwork.scm (%artwork-repository): Update.
* gnu/services/xorg.scm (%default-slim-theme-name): Change to "0.x".
* gnu/system/grub.scm (%background-image): Change to
  GuixSD-fully-black-4-3.svg.

gnu/artwork.scm

@@ -32,9 +32,9 @@
     (method git-fetch)
     (uri (git-reference
           (url "git://git.savannah.gnu.org/guix/guix-artwork.git")
-          (commit "61ae7c8")))
+          (commit "6998d30")))
     (sha256
      (base32
-      "102fxk2l6b0ibry3n430q8ljhwrnbml9qgalzkz6v09r7sx6a532"))))
+      "0k7j3pj9s3zqiqmfkapypssvzx3f12yr0cc2rbzxqfii0b4clp1j"))))
 
 ;;; artwork.scm ends here

gnu/services/xorg.scm

@@ -192,7 +192,7 @@ which should be passed to this script as the first argument.  If not, the
 (define %default-slim-theme-name
   ;; This must be the name of the sub-directory in %DEFAULT-SLIM-THEME that
   ;; contains the actual theme files.
-  "0.8")
+  "0.x")
 
 (define* (slim-service #:key (slim slim)
                        (allow-empty-passwords? #t) auto-login?

gnu/system/grub.scm

@@ -80,7 +80,8 @@
 (define %background-image
   (grub-image
    (aspect-ratio 4/3)
-   (file #~(string-append #$%artwork-repository "/grub/GuixSD-4-3.svg"))))
+   (file #~(string-append #$%artwork-repository
+                          "/grub/GuixSD-fully-black-4-3.svg"))))
 
 (define %default-theme
   ;; Default theme contributed by Felipe López.