fix(Server): Set tls.DEFAULT_ECDH_CURVE to 'auto'

The default value of tls.DEFAULT_ECDH_CURVE is 'prime256v1',
it breaks the connection when certificate is not compatible
with the default curve since node 8.6.0.

To fix this issue, we need set it to 'auto', makes OpenSSL
select the curve automatically.

lib/Server.js

@@ -40,6 +40,16 @@ const createCertificate = require('./utils/createCertificate');
 const validateOptions = require('schema-utils');
 const schema = require('./options.json');
 
+// Workaround for node ^8.6.0, ^9.0.0
+// DEFAULT_ECDH_CURVE is default to prime256v1 in these version
+// breaking connection when certificate is not signed with prime256v1
+// change it to auto allows OpenSSL to select the curve automatically
+// See https://github.com/nodejs/node/issues/16196 for more infomation
+const verMatch = process.version.match(/^v(\d+).(\d+)/);
+if (verMatch && (+verMatch[1] === 9 || (+verMatch[1] === 8 && +verMatch[2] >= 6))) {
+  require('tls').DEFAULT_ECDH_CURVE = 'auto';
+}
+
 const STATS = {
   all: false,
   hash: true,