Update dependencies (#975)

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

@@ -58,6 +58,14 @@ var serverForbiddenKexAlgos = map[string]struct{}{
 	kexAlgoDHGEXSHA256: {}, // server half implementation is only minimal to satisfy the automated tests
 }
 
+// preferredKexAlgos specifies the default preference for key-exchange algorithms
+// in preference order.
+var preferredKexAlgos = []string{
+	kexAlgoCurve25519SHA256,
+	kexAlgoECDH256, kexAlgoECDH384, kexAlgoECDH521,
+	kexAlgoDH14SHA1,
+}
+
 // supportedHostKeyAlgos specifies the supported host-key algorithms (i.e. methods
 // of authenticating servers) in preference order.
 var supportedHostKeyAlgos = []string{
@@ -246,7 +254,7 @@ func (c *Config) SetDefaults() {
 	c.Ciphers = ciphers
 
 	if c.KeyExchanges == nil {
-		c.KeyExchanges = supportedKexAlgos
+		c.KeyExchanges = preferredKexAlgos
 	}
 
 	if c.MACs == nil {