readme: added hhvm support badge
readme: added hhvm support badge

nextras/dbal,nextras/dbal,jasir/dbal,dyamon-cz/nextras-dbal,jasir/dbal,dyamon-cz/nextras-dbal,jasir/dbal,dyamon-cz/nextras-dbal,Mikulas/dbal,Mikulas/dbal,Mikulas/dbal,nextras/dbal