travis: allow failure of MariaDB embedded build
travis: allow failure of MariaDB embedded build

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