[DRE-maint] Bug#848289: ruby-riddle: (build-)depends on mysql-{client, server}

[Andrew Lee (=?UTF-8?Q?=E6=9D=8E=E5=81=A5=E7=A7=8B?=)]

Package: ruby-riddle
Followup-For: Bug #848289

Got confirm from IRC that the MariaDB fail tests cannot be reproduced
on one of our porterbox:
  18:03 < zumbi> AndrewLee: I tried to reproduce, but git built fine in
  a porterbox

I'd roll a new upload from git shortly.

Best regards,
-Andrew