Honor Accept-Encoding header in gzip transcoder

This avoids sending compressed data to clients which do not support
it.

transcoder/minify.go

@@ -6,6 +6,7 @@ import (
 	"github.com/tdewolff/minify/css"
 	"github.com/tdewolff/minify/html"
 	"github.com/tdewolff/minify/js"
+	"net/http"
 )
 
 type Minifier struct {
@@ -24,6 +25,6 @@ func NewMinifier() *Minifier {
 	}
 }
 
-func (t *Minifier) Transcode(w *proxy.ResponseWriter, r *proxy.ResponseReader) error {
+func (t *Minifier) Transcode(w *proxy.ResponseWriter, r *proxy.ResponseReader, headers http.Header) error {
 	return t.m.Minify(r.ContentType(), w, r)
 }