Use Travis's container architecture
Use Travis's container architecture

Builds should start faster and run faster.

Also, test against Ruby 2.2.0.

rochers/fake_braintree,wacii/fake_braintree,rochers/fake_braintree,twalpole/fake_braintree,highfidelity/fake_braintree,twalpole/fake_braintree,foraker/fake_braintree,highfidelity/fake_braintree,foraker/fake_braintree,wacii/fake_braintree