Update stub for spwd (#1372)

Update stub for spwd

- Use `NamedTuple`
- Fix stub for Python 3
  - Some attributes are changed from Python 2
    - `sp_nam` -> `sp_namp`
    - `sp_pwd` -> `sp_pwdp`

stdlib/2/spwd.pyi

@@ -0,0 +1,14 @@
+from typing import List, NamedTuple
+
+struct_spwd = NamedTuple("struct_spwd", [("sp_nam", str),
+                                         ("sp_pwd", str),
+                                         ("sp_lstchg", int),
+                                         ("sp_min", int),
+                                         ("sp_max", int),
+                                         ("sp_warn", int),
+                                         ("sp_inact", int),
+                                         ("sp_expire", int),
+                                         ("sp_flag", int)])
+
+def getspall() -> List[struct_spwd]: ...
+def getspnam(name: str) -> struct_spwd: ...