Change YAML::XS name to YAML::LibYAML in otrs.CheckModules.pl

the YAML::XS module that we need is in a distribution that is called "YAML::LibYAML". 
If you want to install the module you can typically do it by doing "cpan YAML::XS" and it would still work.

However on RHEL or CentOS, if you do 'yum -y instal "perl(YAML::XS)" it will not find the module whereas if you do `yum -y install "perl(YAML::LibYAML)"' it will find it.

Therefore I'd like to change the name we show in CheckModules.pl to YAML::LibYAML.