[PATCH] doc/config/push: use longer "--" line for preformatted example

The example for the push.pushOption config tries to create a preformatted section, but uses only two dashes in its "--" line. In AsciiDoc this is an "open block", with no type; the lines end up jumbled because they're formatted as paragraphs. We need four or more dashes to make it a "listing block" that will respect the linebreaks.

Signed-off-by: Jeff King <peff@peff.net>
---
I noticed this as part our other discussion. The rendered output of
"./doc-diff HEAD^ HEAD" is:

  @@ -4143,15 +4143,20 @@ CONFIGURATION FILE
              repository) to clear the values inherited from a lower priority
              configuration files (e.g.  $HOME/.gitconfig).
   
  -           Example:
  +               Example:
   
  -           /etc/gitconfig push.pushoption = a push.pushoption = b
  +               /etc/gitconfig
  +                 push.pushoption = a
  +                 push.pushoption = b
   
  -           ~/.gitconfig push.pushoption = c
  +               ~/.gitconfig
  +                 push.pushoption = c
   
  -           repo/.git/config push.pushoption = push.pushoption = b
  +               repo/.git/config
  +                 push.pushoption =
  +                 push.pushoption = b
   
  -           This will result in only b (a and c are cleared).
  +               This will result in only b (a and c are cleared).
   
          push.recurseSubmodules
              Make sure all submodule commits used by the revisions to be pushed

 Documentation/config/push.txt | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)