update golang.org/x dependencies

vendor/golang.org/x/crypto/acme/acme.go

@@ -514,7 +514,11 @@ func (c *Client) Accept(ctx context.Context, chal *Challenge) (*Challenge, error
 		return nil, err
 	}
 
-	res, err := c.post(ctx, nil, chal.URI, json.RawMessage("{}"), wantStatus(
+	payload := json.RawMessage("{}")
+	if len(chal.Payload) != 0 {
+		payload = chal.Payload
+	}
+	res, err := c.post(ctx, nil, chal.URI, payload, wantStatus(
 		http.StatusOK,       // according to the spec
 		http.StatusAccepted, // Let's Encrypt: see https://goo.gl/WsJ7VT (acme-divergences.md)
 	))

vendor/golang.org/x/crypto/acme/types.go

@@ -7,6 +7,7 @@ package acme
 import (
 	"crypto"
 	"crypto/x509"
+	"encoding/json"
 	"errors"
 	"fmt"
 	"net/http"
@@ -527,6 +528,16 @@ type Challenge struct {
 	// when this challenge was used.
 	// The type of a non-nil value is *Error.
 	Error error
+
+	// Payload is the JSON-formatted payload that the client sends
+	// to the server to indicate it is ready to respond to the challenge.
+	// When unset, it defaults to an empty JSON object: {}.
+	// For most challenges, the client must not set Payload,
+	// see https://tools.ietf.org/html/rfc8555#section-7.5.1.
+	// Payload is used only for newer challenges (such as "device-attest-01")
+	// where the client must send additional data for the server to validate
+	// the challenge.
+	Payload json.RawMessage
 }
 
 // wireChallenge is ACME JSON challenge representation.