config/guix/system/desktop-bababa-emtec: Fix postgresql.

.config/guix/system/desktop-bababa-emtec.scm

@@ -22,6 +22,7 @@
 (operating-system
   (inherit %bababa/os)
   (packages (cons* nix
+                   postgresql
                    (operating-system-packages %bababa/os)))
   (services (cons*
              (service nix-service-type)
@@ -30,6 +31,6 @@
                       (libvirt-configuration
                        (unix-sock-group "kvm")))
              ;; TODO: Might need 9.6 for Iroha.
-             (postgresql-service)
+             (postgresql-service #:extension-packages (list postgis))
              (service docker-service-type)
              %bababa/services)))