Declare official github home of libraries/unix

Effective immediately, pushing to libraries/unix requires pushing to
ssh://git@github.com/haskell/unix.git. This done now even though there's
no scripted tooling yet as the GitHub repo is already receiving pull requests
(which are getting merged)

packages

@@ -71,7 +71,7 @@ libraries/process            -           -                               -
 libraries/terminfo           -           -                               https://github.com/judah/terminfo.git
 libraries/time               -           -                               http://git.haskell.org/darcs-mirrors/time.git
 libraries/transformers       -           -                               http://git.haskell.org/darcs-mirrors/transformers.git
-libraries/unix               -           -                               -
+libraries/unix               -           -                               ssh://git@github.com/haskell/unix.git
 libraries/Win32              -           -                               https://github.com/haskell/win32.git
 libraries/xhtml              -           -                               https://github.com/haskell/xhtml.git
 nofib                        nofib       -                               -