[PATCH 2 of 2] docker: use official centos5 image

[Mads Kiilerich]

# HG changeset patch
# User Mads Kiilerich <madski at unity3d.com>
# Date 1413474277 -7200
#      Thu Oct 16 17:44:37 2014 +0200
# Node ID 10cd77b15e242f352804c71f4c1233f321cf60fc
# Parent  6cf23144b61e47c7579e4ca42773c24d7f8cf31b
docker: use official centos5 image

I guess it didn't exist when centos5 support was introduced.

diff --git a/contrib/docker/centos5 b/contrib/docker/centos5
--- a/contrib/docker/centos5
+++ b/contrib/docker/centos5
@@ -1,4 +1,4 @@
-FROM saltstack/centos-5-minimal
+FROM centos:centos5
 RUN yum install -y gcc make rpm-build gettext tar
 RUN yum install -y python-devel python-docutils
 # For creating repo meta data