Add newlines to FormatProgress for JSON as well

Commit 060da572d2 has introduced newlines
to streamformatter to help parse Remote API responses. However,
FormatProgress method was omitted from the list of patched methods,
leaving progress messages in, say, /images/create without newlines.

Signed-off-by: Roma Sokolov <sokolov.r.v@gmail.com>

pkg/streamformatter/streamformatter.go

@@ -83,7 +83,7 @@ func (sf *StreamFormatter) FormatProgress(id, action string, progress *jsonmessa
 		if err != nil {
 			return nil
 		}
-		return b
+		return append(b, streamNewlineBytes...)
 	}
 	endl := "\r"
 	if progress.String() == "" {