add '_mapping' to exists_type path (#473)
add '_mapping' to exists_type path (#473)

This adds ‘_mapping’ to the path for exists_type to avoid the
deprecation warning consistent with:
https://github.com/elastic/elasticsearch/commit/a4ea7e72234b480f89e8c59b
b12061be11172db1
elastic/elasticsearch-py,brunobell/elasticsearch-py,brunobell/elasticsearch-py,elastic/elasticsearch-py