Use upstream slack-go/slack again (#1018)

vendor/github.com/slack-go/slack/websocket_files.go

@@ -0,0 +1,49 @@
+package slack
+
+// FileActionEvent represents the File action event
+type fileActionEvent struct {
+	Type           string `json:"type"`
+	EventTimestamp string `json:"event_ts"`
+	File           File   `json:"file"`
+	// FileID is used for FileDeletedEvent
+	FileID string `json:"file_id,omitempty"`
+}
+
+// FileCreatedEvent represents the File created event
+type FileCreatedEvent fileActionEvent
+
+// FileSharedEvent represents the File shared event
+type FileSharedEvent fileActionEvent
+
+// FilePublicEvent represents the File public event
+type FilePublicEvent fileActionEvent
+
+// FileUnsharedEvent represents the File unshared event
+type FileUnsharedEvent fileActionEvent
+
+// FileChangeEvent represents the File change event
+type FileChangeEvent fileActionEvent
+
+// FileDeletedEvent represents the File deleted event
+type FileDeletedEvent fileActionEvent
+
+// FilePrivateEvent represents the File private event
+type FilePrivateEvent fileActionEvent
+
+// FileCommentAddedEvent represents the File comment added event
+type FileCommentAddedEvent struct {
+	fileActionEvent
+	Comment Comment `json:"comment"`
+}
+
+// FileCommentEditedEvent represents the File comment edited event
+type FileCommentEditedEvent struct {
+	fileActionEvent
+	Comment Comment `json:"comment"`
+}
+
+// FileCommentDeletedEvent represents the File comment deleted event
+type FileCommentDeletedEvent struct {
+	fileActionEvent
+	Comment string `json:"comment"`
+}