Release 5.0.37

This release adds a few missing fields to the NestedQuery DSL (see cec324) and the BulkResponseItem (see 42b0e5).

Furthermore, we now use github.com/pkg/errors to enhance error messages, especially on connection problems (see 879b6d). Before this change, you could only see that there was a problem, but the underlying error wasn't available any more. Starting with this release, the error message now contains the underlying error, and you can even access it with github.com/pkg/errors.

Notice that with this change in place you should no longer compare err == elastic.ErrNoClient directly. If you want to filter out connection errors, use the elastic.IsConnErr(err) helper instead.