diff --git a/vendor/github.com/prometheus/client_golang/prometheus/promhttp/delegator_pre_1_8.go b/vendor/github.com/prometheus/client_golang/prometheus/promhttp/delegator_pre_1_8.go
new file mode 100644
index 0000000..8bb9b8b
--- /dev/null
+++ b/vendor/github.com/prometheus/client_golang/prometheus/promhttp/delegator_pre_1_8.go
@@ -0,0 +1,44 @@
+// Copyright 2017 The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// +build !go1.8
+
+package promhttp
+
+import (
+	"io"
+	"net/http"
+)
+
+func newDelegator(w http.ResponseWriter, observeWriteHeaderFunc func(int)) delegator {
+	d := &responseWriterDelegator{
+		ResponseWriter:     w,
+		observeWriteHeader: observeWriteHeaderFunc,
+	}
+
+	id := 0
+	if _, ok := w.(http.CloseNotifier); ok {
+		id += closeNotifier
+	}
+	if _, ok := w.(http.Flusher); ok {
+		id += flusher
+	}
+	if _, ok := w.(http.Hijacker); ok {
+		id += hijacker
+	}
+	if _, ok := w.(io.ReaderFrom); ok {
+		id += readerFrom
+	}
+
+	return pickDelegator[id](d)
+}