Fix build with GHC-7.8
Fix build with GHC-7.8

Fuuzetsu/stack,martin-kolinek/stack,martin-kolinek/stack,deech/stack,juhp/stack,mrkkrp/stack,anton-dessiatov/stack,MichielDerhaeg/stack,AndreasPK/stack,juhp/stack,anton-dessiatov/stack,mrkkrp/stack,deech/stack,AndreasPK/stack,MichielDerhaeg/stack,Fuuzetsu/stack