Support darwin/arm64

[kingdonb]

I ran into the same issue described in this PR:

https://github.com/Automattic/go-search-replace/pull/28/files#diff-76ed074a9305c04054cdebb9e9aad2d818052b07091de1f20cad0bbac34ffb52L8

Looks like this is something that is broken in the base branch. The way I mitigated it is a bit ugly but it works?

Ran a test with a recent go compiler (1.17.2) and the latest version of gox at the ready:

:~/projects/hephy/workflow-cli (master u=)$ go install github.com/mitchellh/gox@latest

:~/projects/hephy/workflow-cli (master u=)$ make build-latest
gox -verbose -ldflags '-X github.com/teamhephy/workflow-cli/version.Version=v2.22.0-f015abf8' -os="linux darwin windows" -arch="amd64 386" -output="_dist/deis-latest-{{.OS}}-{{.Arch}}" .
Number of parallel builds: 7

-->     windows/386: github.com/teamhephy/workflow-cli
-->    darwin/amd64: github.com/teamhephy/workflow-cli
-->     linux/amd64: github.com/teamhephy/workflow-cli
-->       linux/386: github.com/teamhephy/workflow-cli
-->      darwin/386: github.com/teamhephy/workflow-cli
-->   windows/amd64: github.com/teamhephy/workflow-cli

1 errors occurred:
--> darwin/386 error: exit status 2
Stderr: cmd/go: unsupported GOOS/GOARCH pair darwin/386

make: *** [build-latest] Error 1

:~/projects/hephy/workflow-cli (master u=)$ git co support-darwin-arm64
Switched to branch 'support-darwin-arm64'

:~/projects/hephy/workflow-cli (support-darwin-arm64)$ make build-latest
gox -verbose -ldflags '-X github.com/teamhephy/workflow-cli/version.Version=v2.22.0-ea7f801e' -os=darwin -os=linux -os=windows -arch=amd64 -arch=arm64 -osarch=linux/386 -osarch=windows/386 -output="_dist/deis-latest-{{.OS}}-{{.Arch}}" .
Number of parallel builds: 7

-->   windows/amd64: github.com/teamhephy/workflow-cli
-->    darwin/amd64: github.com/teamhephy/workflow-cli
-->     windows/386: github.com/teamhephy/workflow-cli
-->       linux/386: github.com/teamhephy/workflow-cli
-->     linux/amd64: github.com/teamhephy/workflow-cli
-->     linux/arm64: github.com/teamhephy/workflow-cli
-->    darwin/arm64: github.com/teamhephy/workflow-cli