Use .Tag instead of .Version in goreleaser (#40)

We used to use `.Version` in the goreleaser template, but that strips
`v` from the version in the cases we want to use that. Switch to `.Tag`
which leaves it intact.

.goreleaser.yaml

@@ -31,7 +31,7 @@ builds:
 archives:
  - files:
  - no-files-will-match-* # Glob that does not match to create archive with only binaries.
- name_template: "{{ .ProjectName }}_{{ .Version }}_{{ .Os }}_{{ .Arch }}"
+ name_template: "{{ .ProjectName }}_{{ .Tag }}_{{ .Os }}_{{ .Arch }}"
 
 checksum:
  name_template: "checksums.txt"