Update the flag of Martinique to the new official flag

[LucasGault]

Description:

The flag of Martinique currently used in this repository is outdated. The Martinique territorial collectivity has officially adopted a new flag, which is now in use and recognized as the official flag of the territory.

Current Flag:

The flag currently used is the "snake flag" (blue with white cross and snakes), which has historical ties to the colonial era and slavery. This flag is no longer representative of the people of Martinique.

New Official Flag:

The new official flag of Martinique, which was selected after a public consultation in 2019, should replace the old one. The new flag features:

• A red, green, and black design, symbolizing unity, liberty, and the rich heritage of Martinique.

Requested Changes:

• Replace the current Martinique flag with the new official one

Thank you for considering this update!