Bump test projects up to .NET 4.5.2

- aspnet/Testing#248
- xUnit no longer supports .NET 4.5.1
- build tests for desktop .NET only on Windows

test/Microsoft.AspNetCore.ResponseCaching.Tests/Microsoft.AspNetCore.ResponseCaching.Tests.csproj

@@ -3,7 +3,8 @@
   <Import Project="..\..\build\common.props" />
 
   <PropertyGroup>
-    <TargetFrameworks>netcoreapp1.1;net451</TargetFrameworks>
+    <TargetFrameworks>netcoreapp1.1;net452</TargetFrameworks>
+    <TargetFrameworks Condition=" '$(OS)' != 'Windows_NT' ">netcoreapp1.1</TargetFrameworks>
   </PropertyGroup>
 
   <ItemGroup>
@@ -15,5 +16,4 @@
     <PackageReference Include="xunit" Version="2.2.0-*" />
   </ItemGroup>
 
-
 </Project>