update goreleaser config (#460)

Fix goreleaser deprecation warning, add tar.gz format

Author: pgier

.goreleaser.yaml

@@ -32,7 +32,7 @@ builds:
       goarch: '386'
   binary: '{{ .ProjectName }}_v{{ .Version }}'
 archives:
-- format: zip
+- formats: ["zip", "tar.gz"]
   name_template: '{{ .ProjectName }}_{{ .Version }}_{{ .Os }}_{{ .Arch }}'
 checksum:
   name_template: '{{ .ProjectName }}_{{ .Version }}_SHA256SUMS'