Update vendor (mattermost)

vendor/github.com/mattermost/platform/model/slack_attachment.go

@@ -0,0 +1,29 @@
+// Copyright (c) 2017 Mattermost, Inc. All Rights Reserved.
+// See License.txt for license information.
+
+package model
+
+type SlackAttachment struct {
+	Id         int64                   `json:"id"`
+	Fallback   string                  `json:"fallback"`
+	Color      string                  `json:"color"`
+	Pretext    string                  `json:"pretext"`
+	AuthorName string                  `json:"author_name"`
+	AuthorLink string                  `json:"author_link"`
+	AuthorIcon string                  `json:"author_icon"`
+	Title      string                  `json:"title"`
+	TitleLink  string                  `json:"title_link"`
+	Text       string                  `json:"text"`
+	Fields     []*SlackAttachmentField `json:"fields"`
+	ImageURL   string                  `json:"image_url"`
+	ThumbURL   string                  `json:"thumb_url"`
+	Footer     string                  `json:"footer"`
+	FooterIcon string                  `json:"footer_icon"`
+	Timestamp  interface{}             `json:"ts"` // This is either a string or an int64
+}
+
+type SlackAttachmentField struct {
+	Title string      `json:"title"`
+	Value interface{} `json:"value"`
+	Short bool        `json:"short"`
+}