Switch the capybara driver to poltergeist.

It's not obvious how to configure the default driver on a headless server whereas poltergeist works in headless mode out of the box. Spree also uses poltergeist.
Account for Shipping being displayed later in checkout flow

For some reason these specs started failing due to the shipping charge being shown later than the spec expected.
Unsure if this is a bug I inadvertently introduced into the spec or if Spree has changed its behavior, but more likely the former.
Test Cases 2b and 6 are passing again.
Merge pull request #9 from MattFenelon/poltergeist

Switch the capybara driver to poltergeist.
remove unnecessary file
update VERSIONFILE to reflect current branches
add .DS_Store to ignore file
update SPREE_TAXCLOUD_VERSION
Revert "Account for Shipping being displayed later in checkout flow"

This reverts commit af59a7becb9d62913e438768ae6b0ececf716035.