document correct connection error in client documentation

Author: Tethik

docs/client.md

@@ -22,7 +22,7 @@ const client = ldap.createClient({
   url: ['ldap://127.0.0.1:1389', 'ldap://127.0.0.2:1389']
 });
 
-client.on('error', (err) => {
+client.on('connectError', (err) => {
   // handle connection error
 })
 ```