message: chore: define `S3_BUCKET` in Makefile
  We use that variable in the Makefile but we're not defining it, which
  means that maintainers publishing Etcher need to remember to pass that
  as an option.
diff: @@ -26,6 +26,7 @@ APPLICATION_COPYRIGHT = $(shell jq -r '.copyright' package.json)
  APPLICATION_CATEGORY = public.app-category.developer-tools
  APPLICATION_BUNDLE_ID = io.resin.etcher
  APPLICATION_FILES = lib,assets
  +S3_BUCKET = resin-production-downloads
  # Add the current commit to the version if release type is "snapshot"
  RELEASE_TYPE ?= snapshot
  