travis: use latest MariaDB 10.1.x
travis: use latest MariaDB 10.1.x

mroonga/mroonga,mroonga/mroonga,mroonga/mroonga,yoku0825/mroonga,yoku0825/mroonga,yoku0825/mroonga,yoku0825/mroonga,mroonga/mroonga,yoku0825/mroonga,yoku0825/mroonga