How to set CURRENT_TIMESTAMP as a default value in Magento DDL

On 'default' section, change to Varien_Db_Ddl_Table::TIMESTAMP_INIT. So that:

'default'  => Varien_Db_Ddl_Table::TIMESTAMP_INIT

Ref: https://code007.wordpress.com/2014/04/26/magento-how-to-create-a-timestamp-table-column-with-current_timestamp-as-default-value/