Fixed issue #163.

See #163.

This fixes it by converting the 'Scientific' itself instead of going through a Double.

By the way, this is a relatively high-priority issue, since it's affecting the $$$ parsing in network-bitcoin, and people are seeing the wrong amount of money. Would you mind doing a x.y.z+1 release in the near future?

Related issue: https://github.com/wowus/network-bitcoin/issues/10