License tweaks

Author: apalmblad

LICENSE

@@ -3,3 +3,7 @@ License: Free for any use with your own risk!
 OR
 
 The terms of the Public Domain License (http://creativecommons.org/licenses/publicdomain/)
+
+OR 
+
+The terms of the Unlicense, https://spdx.org/licenses/Unlicense.html

ruby-shadow.gemspec

@@ -20,5 +20,5 @@ Gem::Specification.new do |spec|
   spec.required_ruby_version = ['>= 1.8']
   spec.summary               = '*nix Shadow Password Module'
   spec.version               = '2.5.1'
-  spec.license  = "Public Domain License"
+  spec.license  = "Unlicense"
 end