Pyre Bug

Bug description
Pyre can't find a Python Extension Module (.pyd) package in site-package

Reproduction steps
Run pyre with the following .pyre_configuration:

{
  "site_package_search_strategy": "pep561",
  "source_directories": [
    "."
  ],
  "search_path": [
    {
      "site-package": "ujson"
    }
  ],
  "taint_models_path": "Secret",
  "typeshed": "Secret"
}

Expected behavior
It should pass but not warning ƛ Site package does not exist: `ujson`

Logs

pyre check
ƛ Site package does not exist: `ujson`
ƛ No type errors found

Additional context
This may due to pyre do not treat .pyd files(actully all the files that not have .py shuffix) as a package.