Change casing of Windows

Co-authored-by: Jacques Eloff <joeloff@users.noreply.github.com>

Author: dsplaisted

src/Layout/redist/targets/GenerateInstallerLayout.targets

@@ -66,8 +66,8 @@
 
   <Target Name="LayoutDnxShim">
     <ItemGroup>
-      <DnxShimSource Condition="$([MSBuild]::IsOSPlatform('WINDOWS'))" Include="dnx.cmd" />
-      <DnxShimSource Condition="$([MSBuild]::IsOSPlatform('WINDOWS'))" Include="dnx.ps1" />
+      <DnxShimSource Condition="$([MSBuild]::IsOSPlatform('Windows'))" Include="dnx.cmd" />
+      <DnxShimSource Condition="$([MSBuild]::IsOSPlatform('Windows'))" Include="dnx.ps1" />
       <DnxShimSource Condition="!$([MSBuild]::IsOSPlatform('WINDOWS'))" Include="dnx" />
     </ItemGroup>
     <Copy SourceFiles="@(DnxShimSource)" DestinationFolder="$(RedistInstallerLayoutPath)" />