Update vendor slack-go/slack (#1068)

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

@@ -0,0 +1,26 @@
+package slack
+
+// FileBlock defines data that is used to display a remote file.
+//
+// More Information: https://api.slack.com/reference/block-kit/blocks#file
+type FileBlock struct {
+	Type       MessageBlockType `json:"type"`
+	BlockID    string           `json:"block_id,omitempty"`
+	ExternalID string           `json:"external_id"`
+	Source     string           `json:"source"`
+}
+
+// BlockType returns the type of the block
+func (s FileBlock) BlockType() MessageBlockType {
+	return s.Type
+}
+
+// NewFileBlock returns a new instance of a file block
+func NewFileBlock(blockID string, externalID string, source string) *FileBlock {
+	return &FileBlock{
+		Type:       MBTFile,
+		BlockID:    blockID,
+		ExternalID: externalID,
+		Source:     source,
+	}
+}