Update dependencies (#1851)

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

@@ -0,0 +1,28 @@
+package slack
+
+import (
+	"fmt"
+	"net/http"
+)
+
+// StatusCodeError represents an http response error.
+// type httpStatusCode interface { HTTPStatusCode() int } to handle it.
+type StatusCodeError struct {
+	Code   int
+	Status string
+}
+
+func (t StatusCodeError) Error() string {
+	return fmt.Sprintf("slack server error: %s", t.Status)
+}
+
+func (t StatusCodeError) HTTPStatusCode() int {
+	return t.Code
+}
+
+func (t StatusCodeError) Retryable() bool {
+	if t.Code >= 500 || t.Code == http.StatusTooManyRequests {
+		return true
+	}
+	return false
+}