doc: fix typo in tls.md

PR-URL: #15738
Reviewed-By: Daniel Bevenius <daniel.bevenius@gmail.com>
Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

doc/api/tls.md

@@ -474,7 +474,7 @@ changes:
 
 * `socket` {net.Socket} An instance of [`net.Socket`][]
 * `options` {Object}
- * `isServer`: The SSL/TLS protocol is asymetrical, TLSSockets must know if
+ * `isServer`: The SSL/TLS protocol is asymmetrical, TLSSockets must know if
  they are to behave as a server or a client. If `true` the TLS socket will be
  instantiated as a server. Defaults to `false`.
  * `server` {net.Server} An optional [`net.Server`][] instance.