Build Darwin arm64 too (#157)

## Which problem is this PR solving?

- Adds Darwin arm64 binary to the artifacts list
- Fixes #156 

Apparently, this duplicates a change long-ago submitted by another contributor. So credit where due!

Co-authored-by: John <john.dorman@sony.com>

Author: kentquirk

.circleci/config.yml

@@ -70,6 +70,9 @@ jobs:
             - go-build:
                 os: darwin
                 arch: amd64
+            - go-build:
+                os: darwin
+                arch: arm64
             - go-build:
                 os: linux
                 arch: arm64