replace typing Protocol import

Author: Doug Ollerenshaw

allensdk/core/typing.py

@@ -1,8 +1,12 @@
-from typing import _Protocol
+import sys
+if sys.version_info.minor <= 7:  
+    from typing import _Protocol as Protocol
+else:
+    from typing import Protocol
 from abc import abstractmethod
 
 
-class SupportsStr(_Protocol):
+class SupportsStr(Protocol):
     """Classes that support the __str__ method"""
     @abstractmethod
     def __str__(self) -> str: