trivial: build error

Author: kay-kim

source/core/security-ldap.txt

@@ -102,7 +102,7 @@ If you want to continue allowing access by users *not* on the
 ``$external`` database, you must configure :setting:`setParameter`
 :parameter:`authenticationMechanisms` to include ``SCRAM-SHA-1`` and/or
 ``SCRAM-SHA-256`` as appropriate. Users must then specify
-:option:`--authenticationMechanism` ``SCRAM-SHA-1`` or
+``--authenticationMechanisms`` ``SCRAM-SHA-1`` or
 ``SCRAM-SHA-256`` when authenticating.
 
 Deploying LDAP authentication on a replica set