doc: Tweak .texi to avoid po4a-translate infinite loop.

* doc/guix.texi (Requirements): Keep @uref on one line as splitting it
would lead po4a-translate to enter an infinite loop.

doc/guix.texi

@@ -790,8 +790,8 @@ or later;
 @c FIXME: Specify a version number once a release has been made.
 @uref{https://gitlab.com/guile-git/guile-git, Guile-Git}, from August
 2017 or later;
-@item @uref{https://savannah.nongnu.org/projects/guile-json/,
-Guile-JSON} 4.3.0 or later;
+@item @uref{https://savannah.nongnu.org/projects/guile-json/, Guile-JSON}
+4.3.0 or later;
 @item @url{https://www.gnu.org/software/make/, GNU Make}.
 @end itemize