Previously, `HistoricalData.date` was a `date`. When doing date range
calculations such as `HistoricalData.where(
Date.parse('2020-10-20')..Date.parse('2020-10-23'))`, any records
containing 20th or 23rd are included in the result.

However, with `HistoricalData.date` as a timestamp with time zone,
20th would be included (since the time component is assumed to be 00:00)
but 23rd would be excluded.

In order to include both days, we need to use
`.beginning_of_day` and `.end_of_day`. Both methods are time zone aware
and will use the `Time.zone` if available.