update Hackage download URL in bootstrap.sh

Downloading was failing with curl which seems
not do http redirect by default.

This change simple updates the urls from

Hackage 1's http://hackage.haskell.org/packages/archive/$PKG/$VER/$PKG-$VER.tar.gz to
Hackage 2's http://hackage.haskell.org/package/$PKG-$VER/$PKG-$VER.tar.gz

which makes curl happy and downloads work again.
Merge pull request #1655 from juhp/patch-1

update Hackage download URL in bootstrap.sh