add (overwrite with) mypy stubs, if available

stdlib/2.7/pickle.pyi

@@ -0,0 +1,8 @@
+# Stubs for pickle (Python 2)
+
+from typing import Any, IO
+
+def dump(obj: Any, file: IO[str], protocol: int = None) -> None: ...
+def dumps(obj: Any, protocol: int = None) -> str: ...
+def load(file: IO[str]) -> Any: ...
+def loads(str: str) -> Any: ...