Revert "updating the migration script (#54)" (#56)

This reverts commit 3bb7758.

Author: ankita10r

src/main/resources/db/migration/V6__Updating_Default_DateValue.sql

@@ -17,6 +17,5 @@
 -- under the License.
 --
 
-ALTER TABLE m_outbound_messages MODIFY COLUMN submitted_on_date TIMESTAMP NULL DEFAULT CURRENT_TIMESTAMP;
-ALTER TABLE m_outbound_messages MODIFY COLUMN delivered_on_date TIMESTAMP NULL DEFAULT CURRENT_TIMESTAMP;
-
+ALTER TABLE m_outbound_messages MODIFY COLUMN submitted_on_date TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP;
+ALTER TABLE m_outbound_messages MODIFY COLUMN delivered_on_date TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP;