goreleaser: include linux builds in homebrew archive

The homebrew archive only included darwin builds, so the generated
Homebrew cask had no on_linux blocks. When Linux users tried to install
via Linuxbrew, Homebrew couldn't find a download URL, resulting in:

  Error: attempted to use a `Downloadable` without a URL!

Adding linux to the homebrew archive IDs causes GoReleaser to generate
on_linux blocks in the cask with proper download URLs for Linux.

Author: lukasmalkmus

.goreleaser.yaml

@@ -104,6 +104,7 @@ archives:
     name_template: "{{ .ProjectName }}_{{ .Version }}_{{ .Os }}_{{ .Arch }}{{ if .Arm }}v{{ .Arm }}{{ end }}_homebrew"
     ids:
       - darwin
+      - linux
     wrap_in_directory: false
     formats:
       - tar.gz