config: Bump POSIX spec references to IEEE Std 1003.1-2008, 2016 Edition

These references had been using IEEE Std 1003.1, 2004 Edition, but:

  $ curl -s http://pubs.opengroup.org/onlinepubs/009695399/basedefs/xbd_chap08.html | grep -B2 'newer edition'
  <center><font size="2">The Open Group Base Specifications Issue 6<br>
  IEEE Std 1003.1, 2004 Edition<br>
  Copyright &copy; 2001-2004 The IEEE and The Open Group, All Rights reserved.</font></center><center><font color="red">A newer edition of this document exists <a href="http://pubs.opengroup.org/onlinepubs/9699919799/" target="_parent">here</a></font></center>

Shifting to 2016 also syncs us with the 'file' reference in
config-linux.md.  The initial reasoning for the 2004 edition is
unclear to me (more on that in 70858bc, config: Adjust process.args
to cite POSIX's execvp, 2016-05-19, opencontainers#427),

The change-log for the exec page [1] doesn't list any relevant
changes, and skimming a diff of the two HTML pages didn't turn up
anything significant.

Diffing the two HTML pages for environment variables also turned up no
significant changes.  Both definition reference the Portable Character
Set for uppercase letters, digits, and underscore, but the U####
values for those have not changed [2,3].

[1]: http://pubs.opengroup.org/onlinepubs/9699919799/functions/exec.html#tag_16_111_14
[2]: http://pubs.opengroup.org/onlinepubs/009695399/basedefs/xbd_chap06.html#tag_06_01
[3]: http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap06.html#tag_06_01

Signed-off-by: W. Trevor King <[email protected]>

Author: wking

config.md

@@ -839,8 +839,8 @@ Here is a full example `config.json` for reference.
 [procfs_2]: https://www.kernel.org/doc/Documentation/filesystems/proc.txt
 [semver-v2.0.0]: http://semver.org/spec/v2.0.0.html
 [go-environment]: https://golang.org/doc/install/source#environment
-[ieee-1003.1-2001-xbd-c8.1]: http://pubs.opengroup.org/onlinepubs/009695399/basedefs/xbd_chap08.html#tag_08_01
-[ieee-1003.1-2001-xsh-exec]: http://pubs.opengroup.org/onlinepubs/009695399/functions/exec.html
+[ieee-1003.1-2001-xbd-c8.1]: http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap08.html#tag_08_01
+[ieee-1003.1-2001-xsh-exec]: http://pubs.opengroup.org/onlinepubs/9699919799/functions/exec.html
 [mountvol]: http://ss64.com/nt/mountvol.html
 [set-volume-mountpoint]: https://msdn.microsoft.com/en-us/library/windows/desktop/aa365561(v=vs.85).aspx