Updated CMS and Deploy dependencies to 12 preview, and bumped version to 12.0.0-rc

Author: AndyButland

Directory.Packages.props

@@ -12,7 +12,7 @@
   <ItemGroup>
     <PackageVersion Include="NUnit3TestAdapter" Version="4.2.1" />
     <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="17.3.2" />
-    <PackageVersion Include="Umbraco.Cms.Tests" Version="[11.0.0, 12)" />
-    <PackageVersion Include="Umbraco.Deploy.Infrastructure" Version="[11.0.0, 12)" />
+    <PackageVersion Include="Umbraco.Cms.Tests" Version="[12.0.0--rc.preview.1.gfe11f3c, 13)" />
+    <PackageVersion Include="Umbraco.Deploy.Infrastructure" Version="[12.0.0--rc.preview.1.gf3f2138, 13)" />
   </ItemGroup>
 </Project>