Added supported google-cloud-firestore versions

Because Poetry does not yet allow ignoring version dependency numbers I need Firedantic to not depend on a broken version of google-cloud-firestore: python-poetry/poetry#697

For most people this will still install the latest version, but I can pin the version to 2.0.2 with this change until Google fixes the big with the emulator support googleapis/python-firestore#359

pyproject.toml

@@ -14,7 +14,7 @@ packages = [
 python = ">=3.6.1,<4.0"
 pydantic = "^1.8.2"
 grpcio = "^1.36.1"
-google-cloud-firestore = "^2.1.0"
+google-cloud-firestore = "^2.0.1"
 
 [tool.poetry.dev-dependencies]
 isort = "^5.5.2"