Corrected aggregation name to match the example

[ben5556]

Corrected aggregation name from intraday_return to hat_prices to match the aggregation name provided in the example

[lcawl]

To make this change permanently, please update this file:
https://github.com/elastic/elasticsearch/edit/6.2/docs/reference/aggregations/metrics/sum-aggregation.asciidoc

[ben5556]

Thanks @lcawl updated the file and created a PR.

[lcawl]

See elastic/elasticsearch#33786