Correct the case for "MultiPolygon"

[fchabouis]

I thought I was validating a feed with the validator, but I ended up validating the validator with the feed :)

There seems to be a case typo for virtual_areas expected enum : Multipolygon instead of MultiPolygon.

I give you the corresponding feed if you want to test it : https://data-sharing.tier-services.io/tier_grenoble/gbfs/2.2

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[PierrickP]

Hello @fchabouis
Thanks for this PR, i ll merge it.

When i started this project, i took the official schemas from https://github.com/MobilityData/gbfs-json-schema and fixed some parts :)

With MobilityData, we would like to re-integrated fixes from here to https://github.com/MobilityData/gbfs-json-schema and use the schemas from gbfs-json-schema on the validator (like git submodule or something that works, we don't know yet).
But before, they need to re-organize the repository to correctly keep old version of the schema.