First: It's ARMv6.
The Zero uses the original BCM2835 SoC used on the first generation of Pi's and all the other single core models, with a ARM1176JZF-S processor (although the Zero models have ones binned as 1000 Mhz instead of 700).
All ARM11 cores use the ARMv6 instruction set architecture. Since those using ARMv7 or 8 are backward compatible with ARMv6, Raspbian has stuck with that. This is also the reason most of the distros used on the multicore models cannot be used on the Zero -- because they are ARMv7.
I would like update nodejs to the latest version
You can in many cases run code compiled for ARMv7 with an otherwise ARMv6 userland, if the processor itself can run it (meaning, you'd also be using an ARMv7 kernel), which the Zero cannot.