Use href in place of uris following Balanced API v1.1

Yes and no. [They mention](https://docs.balancedpayments.com/1.1/overview/resources/#migrating-to-1-1) "Many attribute names were standardized." and internal `Resource`s classes [use](https://github.com/balanced/balanced-ruby/blob/20fcc4519611dff0258fe2c1fbb02034ca558b0f/lib/balanced/resources/resource.rb#L81-L85) `#find`.