Fix deprecated methods in goreleaser.yml

See: https://github.com/goreleaser/goreleaser/pull/787  
and  
https://github.com/goreleaser/goreleaser/pull/1282

.goreleaser.yml

@@ -3,7 +3,8 @@ release:
   github:
     owner: alecthomas
     name: chroma
-brew:
+brews:
+  -
     install: bin.install "chroma"
 builds:
 - goos:
@@ -18,7 +19,8 @@ builds:
   main: ./cmd/chroma/main.go
   ldflags: -s -w -X main.version={{.Version}} -X main.commit={{.Commit}} -X main.date={{.Date}}
   binary: chroma
-archive:
+archives:
+  -
     format: tar.gz
     name_template: '{{ .Binary }}-{{ .Version }}-{{ .Os }}-{{ .Arch }}{{ if .Arm }}v{{
     .Arm }}{{ end }}'