vendor: Update everything

GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/4620

vendor/golang.org/x/crypto/salsa20/salsa/salsa2020_amd64.s

@@ -5,7 +5,7 @@
 // +build amd64,!appengine,!gccgo
 
 // This code was translated into a form compatible with 6a from the public
-// domain sources in SUPERCOP: http://bench.cr.yp.to/supercop.html
+// domain sources in SUPERCOP: https://bench.cr.yp.to/supercop.html
 
 // func salsa2020XORKeyStream(out, in *byte, n uint64, nonce, key *byte)
 // This needs up to 64 bytes at 360(SP); hence the non-obvious frame size.

vendor/golang.org/x/crypto/salsa20/salsa/salsa20_amd64.go

@@ -13,11 +13,12 @@ package salsa
 func salsa2020XORKeyStream(out, in *byte, n uint64, nonce, key *byte)
 
 // XORKeyStream crypts bytes from in to out using the given key and counters.
-// In and out may be the same slice but otherwise should not overlap. Counter
+// In and out must overlap entirely or not at all. Counter
 // contains the raw salsa20 counter bytes (both nonce and block counter).
 func XORKeyStream(out, in []byte, counter *[16]byte, key *[32]byte) {
 	if len(in) == 0 {
 		return
 	}
+	_ = out[len(in)-1]
 	salsa2020XORKeyStream(&out[0], &in[0], uint64(len(in)), &counter[0], &key[0])
 }

vendor/golang.org/x/crypto/salsa20/salsa/salsa20_ref.go

@@ -203,7 +203,7 @@ func core(out *[64]byte, in *[16]byte, k *[32]byte, c *[16]byte) {
 }
 
 // XORKeyStream crypts bytes from in to out using the given key and counters.
-// In and out may be the same slice but otherwise should not overlap. Counter
+// In and out must overlap entirely or not at all. Counter
 // contains the raw salsa20 counter bytes (both nonce and block counter).
 func XORKeyStream(out, in []byte, counter *[16]byte, key *[32]byte) {
 	var block [64]byte

vendor/golang.org/x/crypto/salsa20/salsa20.go

@@ -3,20 +3,20 @@
 // license that can be found in the LICENSE file.
 
 /*
-Package salsa20 implements the Salsa20 stream cipher as specified in http://cr.yp.to/snuffle/spec.pdf.
+Package salsa20 implements the Salsa20 stream cipher as specified in https://cr.yp.to/snuffle/spec.pdf.
 
 Salsa20 differs from many other stream ciphers in that it is message orientated
 rather than byte orientated. Keystream blocks are not preserved between calls,
 therefore each side must encrypt/decrypt data with the same segmentation.
 
 Another aspect of this difference is that part of the counter is exposed as
-an nonce in each call. Encrypting two different messages with the same (key,
+a nonce in each call. Encrypting two different messages with the same (key,
 nonce) pair leads to trivial plaintext recovery. This is analogous to
 encrypting two different messages with the same key with a traditional stream
 cipher.
 
 This package also implements XSalsa20: a version of Salsa20 with a 24-byte
-nonce as specified in http://cr.yp.to/snuffle/xsalsa-20081128.pdf. Simply
+nonce as specified in https://cr.yp.to/snuffle/xsalsa-20081128.pdf. Simply
 passing a 24-byte slice as the nonce triggers XSalsa20.
 */
 package salsa20 // import "golang.org/x/crypto/salsa20"
@@ -27,8 +27,8 @@ import (
 	"golang.org/x/crypto/salsa20/salsa"
 )
 
-// XORKeyStream crypts bytes from in to out using the given key and nonce. In
-// and out may be the same slice but otherwise should not overlap. Nonce must
+// XORKeyStream crypts bytes from in to out using the given key and nonce.
+// In and out must overlap entirely or not at all. Nonce must
 // be either 8 or 24 bytes long.
 func XORKeyStream(out, in []byte, nonce []byte, key *[32]byte) {
 	if len(out) < len(in) {