[docs] Docs: Little fault in shutil documentation

[Michael Sasser]

Hi,

since Python 3.3 the exception of shutil.copyfile() has been changed
from IOError to OSError. You need to correct this part of the
description in Version 3.3, 3.4 and 3.5:

[...]
Changed in version 3.3: IOError used to be raised instead of OSError.
Added follow_symlinks argument. Now returns dst.
[...]