internal/deepprint: close struct curly parens

Not that it matters, but we were missing a close parens.
It's cheap, so add it.

name    old time/op    new time/op    delta
Hash-8    6.64µs ± 0%    6.67µs ± 1%  +0.42%  (p=0.008 n=9+10)

name    old alloc/op   new alloc/op   delta
Hash-8    1.54kB ± 0%    1.54kB ± 0%    ~     (all equal)

name    old allocs/op  new allocs/op  delta
Hash-8      37.0 ± 0%      37.0 ± 0%    ~     (all equal)

Signed-off-by: Josh Bleecher Snyder <josh@tailscale.com>

internal/deepprint/deepprint.go

@@ -138,6 +138,7 @@ func print(w *bufio.Writer, v reflect.Value, visited map[uintptr]bool) {
 			print(w, v.Field(i), visited)
 			w.WriteString("\n")
 		}
+		w.WriteString("}\n")
 	case reflect.Slice, reflect.Array:
 		if v.Type().Elem().Kind() == reflect.Uint8 && v.CanInterface() {
 			fmt.Fprintf(w, "%q", v.Interface())