Fix wrong apt-get commands in Ubuntu Install doc
Fix wrong apt-get commands in Ubuntu Install doc

Delete duplicate 'apt-get install'
zammad/zammad,zammad/zammad,zammad/zammad,zammad/zammad,monotek/zammad,zammad/zammad,monotek/zammad,monotek/zammad,monotek/zammad,monotek/zammad,zammad/zammad,monotek/zammad