Fix validate_slength, arg.length should be args[0].length
Fix validate_slength, arg.length should be args[0].length

During a puppet run an error will be thrown and a puppet run will fail completely (when using validate_slength):
undefined local variable or method `arg' for #<Puppet::Parser::Scope:0x7f243c236948>
yadavnikhil/puppetlabs-stdlib,DavidS/puppetlabs-stdlib,puppetlabs/puppetlabs-stdlib,fuel-infra/puppetlabs-stdlib,jbondpdx/puppetlabs-stdlib,HelenCampbell/puppetlabs-stdlib