Use the new build env on Travis

more capacity, more ram, more cpu, more wow
Merge pull request #182 from joshk/patch-1

Use the new build env on Travis
Add per-request headers
Merge pull request #183 from stripe/per-request-headers

Add per-request headers
Add the ability to use an api_key for application_fee.refund
Add ability to specify custom headers for application_fee.refund
Add ability to specify custom headers for list_object.create
Merge pull request #184 from stripe/shale/more-per-request-headers

More per request headers
Replace `api_key` with an options hash

For now, only two options are supported: `api_key` and
`idempotency_key`. In the future, we'll be adding support for additional
headers as needed.
Merge pull request #187 from stripe/idempotency

Replace the `api_key` argument with a hash of options
Include stripe account parameter for setting header.
Merge pull request #188 from stripe/wangjohn-stripe-account-header

Include stripe account parameter for setting header.
Bumping version to 1.16.1
Create the file upload api resource (+ bump version)