read-print: Add newline after ‘snippet’ field of ‘origin’.

* guix/read-print.scm (%newline-forms): Add ‘snippet’.

Change-Id: Ibdd654ca68cf9a820b75cdd81e991d747030fa73
Signed-off-by: Ludovic Courtès <ludo@gnu.org>

guix/read-print.scm

@@ -363,6 +363,7 @@ expressions and blanks that were read."
   (vhashq
    ('source '(package))
    ('git-reference '(uri origin))
+   ('snippet '(origin))
    ('sha256 '(origin source package))
    ('arguments '(package))
    ('list '(arguments package))