Prefix include with '@'

According to https://github.com/fluent/fluentd/blob/master/lib%2Ffluent%2Fconfig%2Fv1_parser.rb#L99 update the `include` keyword with prefix `@`

    2014-10-29 07:42:22 +0000 [info]: starting fluentd-0.10.55
    2014-10-29 07:42:22 +0000 [info]: reading config file path="/etc/td-agent/td-agent.conf"
    2014-10-29 07:42:22 +0000 [warn]: 'include' is deprecated. Use '@include' instead