Update stub for grp (#1373)

stdlib/2and3/grp.pyi

@@ -0,0 +1,10 @@
+from typing import List, NamedTuple, Optional
+
+struct_group = NamedTuple("struct_group", [("gr_name", str),
+                                           ("gr_passwd", Optional[str]),
+                                           ("gr_gid", int),
+                                           ("gr_mem", List[str])])
+
+def getgrall() -> List[struct_group]: ...
+def getgrgid(gid: int) -> struct_group: ...
+def getgrnam(name: str) -> struct_group: ...