Bug 20175: [sql_modes] (follow-up) Set a correct default value for club_enrollments...

Bug 20175: [sql_modes] (follow-up) Set a correct default value for club_enrollments.date_created

From comment 6:
"""
Can't recreate database, when creating table structure, I got:
there can be only one TIMESTAMP column with CURRENT_TIMESTAMP in DEFAULT
or ON UPDATE clause

I am on mysql 5.5.59, which is still default in jessie, more timestamp
columns are possible from mysql 5.6.5:
https://dev.mysql.com/doc/relnotes/mysql/5.6/en/news-5-6-5.html
"""

Signed-off-by: Josef Moravec <josef.moravec@gmail.com>
Signed-off-by: Julian Maurice <julian.maurice@biblibre.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>