Merge pull request #10 in TUN/cloudflared from cthuang/tun-829 to master

* commit 'f958536aac58e3be28f1e4a0a01b2c8a216c05b6':
  TUN-829: prefer p256 curve

tlsconfig/tlsconfig.go

@@ -60,7 +60,8 @@ func (f CLIFlags) finishGettingConfig(c *cli.Context, config *tls.Config) *tls.C
 	if c.IsSet(f.RootCA) {
 		config.RootCAs = LoadCert(c.String(f.RootCA))
 	}
-
+	// we optimize CurveP256
+	config.CurvePreferences = []tls.CurveID{tls.CurveP256}
 	return config
 }