Fix typing error (#696)

Signed-off-by: Tushar Goel <tushar.goel.dav@gmail.com>

Author: TG1999

vulnerabilities/improvers/default.py

@@ -1,6 +1,7 @@
 from itertools import chain
 from typing import Iterable
 from typing import List
+from typing import Tuple
 
 from django.db.models.query import QuerySet
 from packageurl import PackageURL
@@ -38,7 +39,7 @@ def get_inferences(self, advisory_data: AdvisoryData) -> Iterable[Inference]:
             )
 
 
-def get_exact_purls(affected_package: AffectedPackage) -> (List[PackageURL], PackageURL):
+def get_exact_purls(affected_package: AffectedPackage) -> Tuple[List[PackageURL], PackageURL]:
     """
     Return a list of affected purls and the fixed package found in the ``affected_package``
     AffectedPackage disregarding any ranges.