In Travis CI, use stack for checking haddocks
In Travis CI, use stack for checking haddocks

harendra-kumar/stack,anton-dessiatov/stack,sjakobi/stack,sjakobi/stack,Heather/stack,Blaisorblade/stack,deech/stack,deech/stack,juhp/stack,MichielDerhaeg/stack,MichielDerhaeg/stack,achernyak/stack,narrative/stack,Heather/stack,phadej/stack,phadej/stack,AndrewRademacher/stack,harendra-kumar/stack,luigy/stack,luigy/stack,martin-kolinek/stack,AndreasPK/stack,AndrewRademacher/stack,narrative/stack,anton-dessiatov/stack,mrkkrp/stack,achernyak/stack,martin-kolinek/stack,Fuuzetsu/stack,Fuuzetsu/stack,AndreasPK/stack,mrkkrp/stack,Blaisorblade/stack,juhp/stack