Merging master to branch (#242)

* Only advance the shard iterator when we accept a result to return

This changes the retriever strategy to only accept the shard iterator
when we have accepted a result to return.  This is for the
asynchronous retriever where multiple threads may contend for the same
iterator slot.  This ensures only the one selected for the response will
advance the shard iterator.

* Release 1.8.5 of the Amazon Kinesis Client for Java (#232)

* Release 1.8.5 of the Amazon Kinesis Client for Java

Release 1.8.5 (September 26, 2017)
* Only advance the shard iterator for the accepted response.  
  This fixes a race condition in the `KinesisDataFetcher` when it's being used to make asynchronous requests.  The shard iterator is now only advanced when the retriever calls `DataFetcherResult#accept()`.
  * PR #230
  * Issue #231