Issue #89. Added note that EU doesn't work with ES 0.19.9.

The problem is this one:

https://github.com/elasticsearch/elasticsearch/issues/2205

This was a bug in ElasticSearch 0.19.9 that was fixed in 0.19.10 so
I added a note to the docs stating ElasticUtils doesn't work with
ElasticSearch 0.19.9.