Fixing error on packages.pp

Fixing this error :
Error: Failed to apply catalog: Parameter unless failed on Exec[add user td-agent to group adm]: 'grep -q "adm\S*td-agent" /etc/group' is not qualified and no path was specified. Please qualify the command or specify a path. at /etc/puppet/modules/fluentd/manifests/packages.pp:51
Wrapped exception:
'grep -q "adm\S*td-agent" /etc/group' is not qualified and no path was specified. Please qualify the command or specify a path.
Merge pull request #11 from Seraf/develop

Fixing error on packages.pp