Fetch branch builds

Fetch branch builds. There's an integration test that assumes environment variables BUILDBOX_API_KEY and BUILDBOX_ACCOUNT are set appropriately.

I've been running tests on command line with 
BUILDBOX_API_KEY=<my key> BUILDBOX_ACCOUNT=envato-marketplaces rspec
because I don't want to have my key in a file anywhere, given that this is open source.

Can you think of a better way?