fix asciidoc,xmlto are missing for CentOS

asciidoc: command not found; xmlto: command not found;

shadowsocks.sh

@@ -102,7 +102,7 @@ if [ "$OS" == 'CentOS' ]; then
     done
     AddUser_shadowsocks
     Iptables_set
-    for Package in wget unzip openssl-devel gcc swig python python-devel python-setuptools autoconf libtool libevent automake make curl curl-devel zlib-devel perl perl-devel cpio expat-devel gettext-devel git
+    for Package in wget unzip openssl-devel gcc swig python python-devel python-setuptools autoconf libtool libevent automake make curl curl-devel zlib-devel perl perl-devel cpio expat-devel gettext-devel git asciidoc xmlto
     do
         yum -y install $Package
     done