fix(release): rename folder to directory for GoReleaser v2

GoReleaser v2 renamed the `folder` field to `directory` in the brews
config section.

Author: dedene

.goreleaser.yml

@@ -53,7 +53,7 @@ brews:
     repository:
       owner: dedene
       name: homebrew-tap
-    folder: Formula
+    directory: Formula
     homepage: https://github.com/dedene/irail-cli
     description: CLI for Belgian railway (NMBS/SNCB) schedules
     license: MIT