Minor revision of the text.

Doc/lib/libposix.tex

@@ -88,8 +88,8 @@ export statements to the command string for \function{system()} or
 \note{The \refmodule{os} module provides an alternate
 implementation of \code{environ} which updates the environment on
 modification.  Note also that updating \code{os.environ} will render
-this dictionary obsolete.  Use of the \refmodule{os} for this is
-recommended over direct access to the \module{posix} module.}
+this dictionary obsolete.  Use of the \refmodule{os} module version of
+this is recommended over direct access to the \module{posix} module.}
 \end{datadesc}
 
 Additional contents of this module should only be accessed via the