Bump Go versions for Travis, fix tests

Replace gometalinter with golangci-lint.

Fix system tests (wheezy is gone, replace with stretch).

Fix linter warnings.

deb/deb.go

@@ -11,7 +11,7 @@ import (
 	"strings"
 
 	"github.com/h2non/filetype/matchers"
-	"github.com/mkrautz/goar"
+	ar "github.com/mkrautz/goar"
 	"github.com/pkg/errors"
 
 	"github.com/aptly-dev/aptly/pgp"

deb/format.go

@@ -134,7 +134,9 @@ func isMultilineField(field string, isRelease bool) bool {
 	return false
 }
 
-// Write single field from Stanza to writer
+// Write single field from Stanza to writer.
+//
+//nolint: interfacer
 func writeField(w *bufio.Writer, field, value string, isRelease bool) (err error) {
 	if !isMultilineField(field, isRelease) {
 		_, err = w.WriteString(field + ": " + value + "\n")