doc: describe when a tls server emits 'close'

PR-URL: https://github.com/nodejs/node/pull/9665
Reviewed-By: Roman Reiss <me@silverwind.io>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: Myles Borins <myles.borins@gmail.com>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>
Reviewed-By: Brian White <mscdex@mscdex.net>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>

doc/api/tls.md

@@ -365,7 +365,7 @@ added: v0.3.2
 The `server.close()` method stops the server from accepting new connections.
 
 This function operates asynchronously. The `'close'` event will be emitted
-when the the server is finally closed.
+when the server has no more open connections.
 
 ### server.connections
 <!-- YAML