Slightly simplify utils.compileFileWithRecipe

This commit should be equivalent, no semantic changes just simplified
the notation.

Upgrade protobuf to v3.9.1 on the CI

Now we can have the same version on both drone.io and AppVeyor, see PR arduino#329 for the details.

Add s3 upload support in .goreleaser.yml via `blob` configuration

- used blob configuration instead of deprecated s3 one. this requires
adding a AWS_DEFAULT_REGION env var to the drone step (toghether with
the IAM credentials), because this
property is missing in the blob config