updated manifest file

plugin_installer/manifest.ini

 [info]
 name: Plugin Installer
 short_name: plugin_installer
-version: 0.13.0
+version: 0.13.1
 description: Install and upgrade plugins from ftp
 authors: Denis Fomin <fominde@gmail.com>
  Yann Leboulanger <asterix@lagaule.org>
+ Thilo Molitor <thilo@eightysoft.de>
 homepage: http://trac-plugins.gajim.org/wiki/PluginInstallerPlugin
 min_gajim_version: 0.16.10