Removed dependency cycle

Removed dependency cycle which failing the module under puppet 3.4: 
Error: Could not apply complete catalog: Found 1 dependency cycle:
(Exec[concat_/etc/exports] => Concat[/etc/exports] => Service[nfs-kernel-server] => Class[Nfs::Server::Debian] => Concat[/etc/exports] => Exec[concat_/etc/exports])
Try the '--graph' option and opening the resulting '.dot' file in OmniGraffle or GraphViz