document that it doesn't work with ES 0.19.9

[willkg]

@rlr went through and tested Kitsune (which uses elasticutils) with 0.19.8, 0.19.9, 0.19.10, and 0.19.11:

https://bugzilla.mozilla.org/show_bug.cgi?id=811300

Conclusion is that Kitsune tests fail with 0.19.9. It's probably the case that elasticutils doesn't work with 0.19.9, too.

This issue is about verifying that statement and noting incompatibility in the docs.

[willkg]

The problem is this one:

elastic/elasticsearch#2205

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

Fixed in fad6288.