Merge branch 'tls1.2' into 'master'

Set minimum TLS version to 1.2

See merge request tslocum/twins!1

server.go

@@ -493,6 +493,7 @@ func listen(address string) {
 	tlsConfig := &tls.Config{
 		ClientAuth:         tls.RequestClientCert,
 		GetCertificate:     getCertificate,
+		MinVersion:         tls.VersionTLS12,
 		InsecureSkipVerify: true,
 	}