Update vendor (github.com/mattermost)

vendor/github.com/mattermost/mattermost-server/model/message_export.go

@@ -0,0 +1,19 @@
+// Copyright (c) 2017-present Mattermost, Inc. All Rights Reserved.
+// See License.txt for license information.
+
+package model
+
+type MessageExport struct {
+	ChannelId          *string
+	ChannelDisplayName *string
+
+	UserId    *string
+	UserEmail *string
+	Username  *string
+
+	PostId       *string
+	PostCreateAt *int64
+	PostMessage  *string
+	PostType     *string
+	PostFileIds  StringArray
+}