Fix typo in spec test
Fix typo in spec test

This commit fixes a typo in dhcp spec tests. Specifically, Dawin is corrected to Darwin.

archii/puppetlabs-dhcp,ocadotechnology/puppetlabs-dhcp,archii/puppetlabs-dhcp,puppetlabs/puppetlabs-dhcp,ocadotechnology/puppetlabs-dhcp,puppetlabs/puppetlabs-dhcp