doc: fix typo in tls.md

PR-URL: https://github.com/nodejs/node/pull/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

@@ -467,7 +467,7 @@ added: v0.11.4
 
 * `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.