Add ps_credential dsl method to dsc_script

You can now do the following:

```ruby
dsc_script 'create-foo-user' do
  code <<-EOH
     User FooUser00
     {
       Ensure = "Present"
       UserName = 'FooUser00'
       Password = #{ps_credential('FooBarBaz1!')}
     }
  EOH
  configuration_data <<-EOH
    @{
      AllNodes = @(
        @{
          NodeName = "localhost";
          CertificateID = 'A8DB81D8059F349F7EF19104399B898F701D4167'
        }
      )
    }
  EOH
end
```

1 files changed, 2 insertions, 0 deletions

diff --git a/lib/chef/resource/dsc_script.rb b/lib/chef/resource/dsc_script.rb
index 2877f61eb4..c3602fa60e 100644
--- a/lib/chef/resource/dsc_script.rb
+++ b/lib/chef/resource/dsc_script.rb
@@ -17,10 +17,12 @@
 #
 
 require 'chef/exceptions'
+require 'chef/dsl/powershell'
 
 class Chef
   class Resource
     class DscScript < Chef::Resource
+      include Chef::DSL::Powershell
 
       provides :dsc_script, os: "windows"