Add support for building on and for Darwin:arm64

[mhagger]

Update to Go 1.16.3, which includes support for Darwin:arm64. On the other hand, Darwin:386 is no longer supported, so remove that from the list of releases that we build.

Fixes #68

/cc @dbast, who requested this.

[dbast]

Nice. Thanks!

Calling make with system pre-installed go 1.16.3 works and the binaries also work. Also cross compiled binaries work, compiled on linux amd64 and tested on Apple M1 hardware make GOOS=darwin GOARCH=arm64.

Calling make with no pre-installed go, downloads go, but then fails with:

go: inconsistent vendoring in /home/daniel/git-sizer:
	github.com/davecgh/[email protected]: is explicitly required in go.mod, but not marked as explicit in vendor/modules.txt
	github.com/spf13/[email protected]: is explicitly required in go.mod, but not marked as explicit in vendor/modules.txt
	github.com/stretchr/[email protected]: is explicitly required in go.mod, but not marked as explicit in vendor/modules.txt
	gopkg.in/[email protected]: is explicitly required in go.mod, but not marked as explicit in vendor/modules.txt

	To ignore the vendor directory, use -mod=readonly or -mod=mod.
	To sync the vendor directory, run:
		go mod vendor
mkdir -p bin
/home/daniel/git-sizer/script/go build -ldflags "-X main.BuildVersion=v1.3.0-14-g57e3d3e" -o bin/git-sizer github.com/github/git-sizer
go: inconsistent vendoring in /home/daniel/git-sizer:
	github.com/davecgh/[email protected]: is explicitly required in go.mod, but not marked as explicit in vendor/modules.txt
	github.com/spf13/[email protected]: is explicitly required in go.mod, but not marked as explicit in vendor/modules.txt
	github.com/stretchr/[email protected]: is explicitly required in go.mod, but not marked as explicit in vendor/modules.txt
	gopkg.in/[email protected]: is explicitly required in go.mod, but not marked as explicit in vendor/modules.txt

	To ignore the vendor directory, use -mod=readonly or -mod=mod.
	To sync the vendor directory, run:
		go mod vendor
make: *** [Makefile:29: bin/git-sizer] Error 1

After calling vendor/go1.16.3/go/bin/go mod vendor, make also works with the script/install-vendored-go installed go.

[dbast]

Hm... seems like some effort was put into the Makefile + shell scripts in script. Other option would be going for the setup-go + goreleaser Github actions in order to automatic compile/test/release binaries, see e.g. https://github.com/hhatto/gocloc/blob/master/.github/workflows/release.yml and other projects with similar setup.

[mhagger]

@dbast: Thanks for the help! I just pushed some more changes to this branch that will hopefully improve things. Please let me know if this does it for you.

[dbast]

Tested and Makefile looks much cleaner now.

[dbast]

Thanks for working on this and merging the update.

Care to tag a new minor release, which makes it easier for those who package git-sizer for various distributions? Thx!