2.5.1 (2016-07-19)

• [IMPROVED] Made the 429 response code backoff optional and configurable. To enable the backoff add
  an instance of a Replay429Interceptor with the desired number of retries and initial backoff:
  ClientBuilder.account("example").interceptors(new Replay429Interceptor(retries, initialBackoff))
  A default instance is available using 3 retries and starting with a 250 ms backoff:
  Replay429Interceptor.WITH_DEFAULTS. To replicate the backoff of version 2.5.0 create an instance
  using new Replay429Interceptor(10, 250l).
• [FIX] Fixed places where streams where not closed and could cause connections to leak.