adds signature to card_stream_modern.rb and ports over some features of card_stream.rb
CRITICAL FIX: AVS fails for people with a flat number,
Remove CardStream legacy and replace it with CardStream Modern gateway
Digest::Digest is deprecated.

[ref ruby/ruby#446]
travisci: test on 2.1.0
Better travis ci
Merge pull request #1023 from Shopify/digest_warn

Digest::Digest is deprecated.
Moneybookers - Do not raise if credential2 hasn't been passed in, acknowledge will fail instead
Merge pull request #1024 from Shopify/remove_moneybookers_raising_without_credential2

Moneybookers - Do not raise if credential2 hasn't been passed in
Fix CI

Exclude rails 23 + ruby 2.1.0 on tests
Only display travis status from master.
Merge pull request #1021 from Shopify/cardstream_signature

Cardstream P3 upgrade
Update CHANGELOG for 1.42.5 bump
Bump AM version to 1.42.5
Adjust conekta integration to use :login
Update few asserts in Conekta remote tests
Update fixtures and fix one more test
Merge pull request #1031 from Shopify/fix_conekta

Change Conekta gateway to use :login instead of :key
Litle: Truncate order_id

Litle requires the order_id to be a maximum of 25 characters.

Closes #1034.
Conekta: Fix #refund; respect :currency

Refund parameters were backwards causing "money amount must be a
positive Integer in cents.".

Currency parameter was not being respected.

Closes #1015.