lib update crashes when no libs are installed

[pelikhan]

• install fresh platform

• run "lib update"

  $ platformio lib update
  Traceback (most recent call last):
  File "/Library/Python/2.7/site-packages/platformio-0.7.0-py2.7.egg/platformio/main.py", line 64, in main
  cli()
  File "/Library/Python/2.7/site-packages/click-3.3-py2.7.egg/click/core.py", line 610, in call
  return self.main(_args, *_kwargs)
  File "/Library/Python/2.7/site-packages/click-3.3-py2.7.egg/click/core.py", line 590, in main
  rv = self.invoke(ctx)
  File "/Library/Python/2.7/site-packages/click-3.3-py2.7.egg/click/core.py", line 936, in invoke
  return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/Library/Python/2.7/site-packages/click-3.3-py2.7.egg/click/core.py", line 936, in invoke
  return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/Library/Python/2.7/site-packages/click-3.3-py2.7.egg/click/core.py", line 782, in invoke
  return ctx.invoke(self.callback, *_ctx.params)
  File "/Library/Python/2.7/site-packages/click-3.3-py2.7.egg/click/core.py", line 416, in invoke
  return callback(_args, **kwargs)
  File "/Library/Python/2.7/site-packages/platformio-0.7.0-py2.7.egg/platformio/commands/lib.py", line 143, in lib_update
  lib_names = lm.get_installed()
  File "/Library/Python/2.7/site-packages/platformio-0.7.0-py2.7.egg/platformio/libmanager.py", line 36, in get_installed
  for item in listdir(self.lib_dir):
  OSError: [Errno 2] No such file or directory: 'YYYYYYY/.platformio/lib'

[ivankravets]

Thanks a lot for report!
I'm going to release new version 0.7.1with bug fixes tomorrow.