added vendor

vendor/github.com/gorilla/websocket/tls_handshake.go

@@ -0,0 +1,21 @@
+//go:build go1.17
+// +build go1.17
+
+package websocket
+
+import (
+	"context"
+	"crypto/tls"
+)
+
+func doHandshake(ctx context.Context, tlsConn *tls.Conn, cfg *tls.Config) error {
+	if err := tlsConn.HandshakeContext(ctx); err != nil {
+		return err
+	}
+	if !cfg.InsecureSkipVerify {
+		if err := tlsConn.VerifyHostname(cfg.ServerName); err != nil {
+			return err
+		}
+	}
+	return nil
+}