Credit Card expiry comparison logic incorrect outside of UTC - would fail with card_expired method if CC is expiring this month

Fixes #3578
capybara 2.1 requires visible: false to match elements in <head>, and other invisible elements
Clear tax adjustments only in TaxRate#adjust

It doesn't make sense to remove all line item adjustments from
TaxRate#adjust because price adjustments might come from other classes
such as ShippingMethod and PromotionAction

Fixes #2981
Fix order deprecation on association.
Fix deprecation warnings by using line_item_adjustment_totals.
Add sample gem to travis config.
[backend] Js lint. Fixes #3544