make-ring: don't build contrib in parallel

Making contrib with the -j option changes the order of the linker
flags in some cases and causes the build of the daemon to fail
during linking.

Reviewed-by: Alexandre Viau <alexandre.viau@savoirfairelinux.com>
Change-Id: I79648cbb676e977679498c3078caeec4aaf1330e

scripts/install.sh

@@ -61,7 +61,7 @@ cd contrib
 mkdir -p native
 cd native
 ../bootstrap
-make -j2
+make
 cd "${DAEMON}"
 ./autogen.sh
 if $global; then