diff --git a/unum/vendor/golang.org/x/net/http2/headermap.go b/unum/vendor/golang.org/x/net/http2/headermap.go
new file mode 100644
index 0000000..c2805f6
--- /dev/null
+++ b/unum/vendor/golang.org/x/net/http2/headermap.go
@@ -0,0 +1,78 @@
+// Copyright 2014 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package http2
+
+import (
+	"net/http"
+	"strings"
+)
+
+var (
+	commonLowerHeader = map[string]string{} // Go-Canonical-Case -> lower-case
+	commonCanonHeader = map[string]string{} // lower-case -> Go-Canonical-Case
+)
+
+func init() {
+	for _, v := range []string{
+		"accept",
+		"accept-charset",
+		"accept-encoding",
+		"accept-language",
+		"accept-ranges",
+		"age",
+		"access-control-allow-origin",
+		"allow",
+		"authorization",
+		"cache-control",
+		"content-disposition",
+		"content-encoding",
+		"content-language",
+		"content-length",
+		"content-location",
+		"content-range",
+		"content-type",
+		"cookie",
+		"date",
+		"etag",
+		"expect",
+		"expires",
+		"from",
+		"host",
+		"if-match",
+		"if-modified-since",
+		"if-none-match",
+		"if-unmodified-since",
+		"last-modified",
+		"link",
+		"location",
+		"max-forwards",
+		"proxy-authenticate",
+		"proxy-authorization",
+		"range",
+		"referer",
+		"refresh",
+		"retry-after",
+		"server",
+		"set-cookie",
+		"strict-transport-security",
+		"trailer",
+		"transfer-encoding",
+		"user-agent",
+		"vary",
+		"via",
+		"www-authenticate",
+	} {
+		chk := http.CanonicalHeaderKey(v)
+		commonLowerHeader[chk] = v
+		commonCanonHeader[v] = chk
+	}
+}
+
+func lowerHeader(v string) string {
+	if s, ok := commonLowerHeader[v]; ok {
+		return s
+	}
+	return strings.ToLower(v)
+}