Wrap Zlib::BufError in ActiveMerchant::InvalidResponseError

This wraps `Zlib::BufError` into a more friendly `ActiveMerchantError `. This will now be retriable and rescuable at a higher level.

Ref.: https://github.com/Shopify/shopify/issues/12353

@jduff @costford for review

Paired with @gmalette