Typo: Update ldap.adoc

there is no word like 'byusing'. I fixed 'byusing' to 'by using'.

docs/modules/ROOT/pages/servlet/authentication/passwords/ldap.adoc

@@ -614,7 +614,7 @@ You need only supply the domain name and an LDAP URL that supplies the address o
 
 [NOTE]
 ====
-It is also possible to obtain the server's IP address byusing a DNS lookup.
+It is also possible to obtain the server's IP address by using a DNS lookup.
 This is not currently supported, but hopefully will be in a future version.
 ====