install: Use set -x when installing node, shellcheck, shfmt, tx.

This makes it clearer which step failed if there’s an error.

Signed-off-by: Anders Kaseorg <anders@zulip.com>

scripts/lib/install-node

@@ -22,6 +22,7 @@ check_version() {
 }
 
 if ! check_version 2>/dev/null; then
+    set -x
     tmpdir="$(mktemp -d)"
     trap 'rm -r "$tmpdir"' EXIT
     cd "$tmpdir"