GUACAMOLE-234: Correct LDAP filter mispelling.

extensions/guacamole-auth-ldap/src/main/java/org/apache/guacamole/auth/ldap/group/UserGroupService.java

@@ -87,7 +87,7 @@ public class UserGroupService {
 
         // Read any object as a group if LDAP is not being used for connection
         // storage (guacConfigGroup)
-        return new EqualityNode("objectCalss","*");
+        return new EqualityNode("objectClass","*");
 
     }