try to fix build fail

htdocs/install/mysql/tables/llx_webhook_target_extrafields.sql

@@ -16,7 +16,7 @@
 create table llx_webhook_target_extrafields
 (
   rowid                     integer AUTO_INCREMENT PRIMARY KEY,
-  tms                       timestamp,
+  tms                       timestamp DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
   fk_object                 integer NOT NULL,
   import_key                varchar(14)                          		-- import key
 ) ENGINE=innodb;