Fix incorrect date typing in signatures

[montezdesousa]

openbb.economy.macro(start_date="2019-01-01", end_date="2019-12-31")
economy/macro -s 2019-01-01 -e 2019-12-31

Description

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Checklist:

• Update our Hugo documentation following these guidelines.
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Others

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[Chavithra]

Looks ok to me.

[montezdesousa]

Looks ok to me.

Looks ok to me.

Had to make some changes due to mypy