Fix panic with debug_http_headers

doh-server/server.go

@@ -114,7 +114,7 @@ func (s *Server) handlerFunc(w http.ResponseWriter, r *http.Request) {
 	}
 
 	for _, header := range s.conf.DebugHTTPHeaders {
-		if value:= r.Header.Get(header); value != "" {
+		if value := r.Header.Get(header); value != "" {
 			log.Printf("%s: %s\n", header, value)
 		}
 	}