haskell/yi: Build against vty 4.7.5.

Probably jailbreak would do as well, but the version constraints are:

vty >= 4.7.4 && <5

I suppose the upcoming release of Yi will fix this, so I'm not using
jailbreak here (apart from the fact that Yi doesn't build successfully
using VTY >= 5).

Thanks to @bb010g for reporting.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>