arm64 supported architecture

[gschier]

We recently had a user on a Raspberry PI try to install the railway.app cli but it failed to find the correct binary for their arch: railwayapp/cli#94

From their posted issue, the error is: Installation is not supported for this architecture: arm64

Upon first glance, it seems like their process.arch returns amd64, which is not listed in this map

go-npm/src/index.js

Lines 13 to 18 in ff6d922

	// Mapping from Node's `process.arch` to Golang's `$GOARCH`
	const ARCH_MAPPING = {
	"ia32": "386",
	"x64": "amd64",
	"arm": "arm"
	};

Thoughts on whether adding this would be okay? It looks like arm64 is valid for both Node and Go.
https://nodejs.org/api/process.html#process_process_arch
https://gist.github.com/asukakenji/f15ba7e588ac42795f421b48b8aede63#a-list-of-valid-goarch-values

[esgott]

Same issue happens on the M1 Macs.