[MINOR] fix doc in `EXTRACT(field FROM source)

[Ted-Jiang]

Closes #.

Rationale for this change

Sorry for my carelessness.

❯ select date_part('week', to_timestamp('2020-09-08T12:00:12+00:00'))
;
+-----------------------------------------------------------------------+
| datepart(Utf8("week"),totimestamp(Utf8("2020-09-08T12:00:12+00:00"))) |
+-----------------------------------------------------------------------+
| 37                                                                    |
+-----------------------------------------------------------------------+
1 row in set. Query took 0.005 seconds.
❯

week result should be 37.

What changes are included in this PR?

Are there any user-facing changes?

[jackwener]

🤣