posts:nginx: Export HOME=/ to spawn-fcgi process for gitweb

posts:nginx: Export HOME=/ to spawn-fcgi process for gitweb

Since Git's 96b9e0e (config: treat user and xdg config permission
problems as errors, 2012-10-13), `git` dies with:

  fatal: unable to access '/root/.config/git/config': Permission denied

when it doesn't have access to the HOME directory where it think's its
config files are stored.  Running an strace shows:

  access("/root/.config/git/config", R_OK) = -1 EACCES (Permission denied)

Since this error is fatal, we need to set the HOME environment
variable to somewhere where the server process (the `nginx` user on my
box) *does* have access.  Regardless of the user, `HOME=/` should be
pretty safe ;).