build tests for net45 and let codecov run it

tests/CodeCoverage/CodeCoverage.cmd

@@ -12,7 +12,7 @@ cd ..
 cd ..
 
 rem The -threshold options prevents this taking ages...
-tests\CodeCoverage\OpenCover.4.6.519\tools\OpenCover.Console.exe -target:"dotnet.exe" -targetargs:"test tests\ImageSharp.Tests\ImageSharp.Tests.csproj -c Release -f net451 -r win7-x64" -threshold:10 -register:user -filter:"+[ImageSharp*]*" -excludebyattribute:*.ExcludeFromCodeCoverage* -hideskipped:All -returntargetcode -output:.\ImageSharp.Coverage.xml
+tests\CodeCoverage\OpenCover.4.6.519\tools\OpenCover.Console.exe -target:"dotnet.exe" -targetargs:"test tests\ImageSharp.Tests\ImageSharp.Tests.csproj -c Release -f net45" -threshold:10 -register:user -filter:"+[ImageSharp*]*" -excludebyattribute:*.ExcludeFromCodeCoverage* -hideskipped:All -returntargetcode -output:.\ImageSharp.Coverage.xml
 
 if %errorlevel% neq 0 exit /b %errorlevel%
 

tests/ImageSharp.Tests/ImageSharp.Tests.csproj

@@ -1,6 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFramework>netcoreapp1.0</TargetFramework>
+    <TargetFrameworks>netcoreapp1.0;net45</TargetFrameworks>
+    <RuntimeIdentifier>win7-x64</RuntimeIdentifier>
     <AllowUnsafeBlocks>True</AllowUnsafeBlocks>
   </PropertyGroup>
   <ItemGroup>
@@ -17,6 +18,11 @@
     <ProjectReference Include="..\..\src\ImageSharp.Processing\ImageSharp.Processing.csproj" />
     <ProjectReference Include="..\..\src\ImageSharp\ImageSharp.csproj" />
   </ItemGroup>
+  <ItemGroup Condition=" '$(TargetFramework)' == 'net45' ">
+    <Reference Include="System.Runtime" />
+    <Reference Include="System" />
+    <Reference Include="Microsoft.CSharp" />
+  </ItemGroup>
   <ItemGroup>
     <Service Include="{82a7f48d-3b50-4b1e-b82e-3ada8210c358}" />
   </ItemGroup>