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 +40,13 @@ 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
+require('tls').DEFAULT_ECDH_CURVE = 'auto';
+
 const STATS = {
   all: false,
   hash: true,