os: Update for builtin "struct" renamed to "ustruct".

os/metadata.txt

@@ -1,5 +1,5 @@
 srctype = micropython-lib
 type = package
-version = 0.2
+version = 0.2.1
 author = Paul Sokolovsky
 depends = libc, errno, stat

os/os/__init__.py

@@ -1,6 +1,6 @@
 import ffi
 import array
-import struct
+import ustruct as struct
 import errno
 import stat as stat_
 import _libc

os/setup.py

@@ -6,7 +6,7 @@ from setuptools import setup
 
 
 setup(name='micropython-os',
-      version='0.2',
+      version='0.2.1',
       description='os module for MicroPython',
       long_description="This is a module reimplemented specifically for MicroPython standard library,\nwith efficient and lean design in mind. Note that this module is likely work\nin progress and likely supports just a subset of CPython's corresponding\nmodule. Please help with the development if you are interested in this\nmodule.",
       url='https://github.com/micropython/micropython/issues/405',