Update golang x/crypto dependencies (#2923)

vendor/golang.org/x/crypto/ssh/messages.go

@@ -23,10 +23,6 @@ const (
 	msgUnimplemented = 3
 	msgDebug         = 4
 	msgNewKeys       = 21
-
-	// Standard authentication messages
-	msgUserAuthSuccess = 52
-	msgUserAuthBanner  = 53
 )
 
 // SSH messages:
@@ -137,6 +133,18 @@ type userAuthFailureMsg struct {
 	PartialSuccess bool
 }
 
+// See RFC 4252, section 5.1
+const msgUserAuthSuccess = 52
+
+// See RFC 4252, section 5.4
+const msgUserAuthBanner = 53
+
+type userAuthBannerMsg struct {
+	Message string `sshtype:"53"`
+	// unused, but required to allow message parsing
+	Language string
+}
+
 // See RFC 4256, section 3.2
 const msgUserAuthInfoRequest = 60
 const msgUserAuthInfoResponse = 61