[MINOR][DOCS] Fix wrong data types in JSON Datasets example.

## What changes were proposed in this pull request?

This PR fixes the `age` data types from `integer` to `long` in `SQL Programming Guide: JSON Datasets`.

## How was this patch tested?

Manual.

Author: Dongjoon Hyun <dongjoon@apache.org>

Closes #12290 from dongjoon-hyun/minor_fix_type_in_json_example.