[SL.Core] Update tests to target netcoreapp2.1

tests/CodeCoverage/CodeCoverage.cmd

@@ -10,7 +10,7 @@ cd ..
 dotnet restore SixLabors.Core.sln
 dotnet build SixLabors.Core.sln --no-incremental -c release /p:codecov=true
 
-tests\CodeCoverage\OpenCover.4.6.519\tools\OpenCover.Console.exe -target:"dotnet.exe" -targetargs:"test tests\SixLabors.Core.Tests\SixLabors.Core.Tests.csproj --no-build -c release" -searchdirs:"tests\SixLabors.Core.Tests\bin\Release\netcoreapp1.1" -register:user -output:.\SixLabors.Core.Coverage.xml -hideskipped:All -returntargetcode -oldStyle -filter:"+[SixLabors.*]*" 
+tests\CodeCoverage\OpenCover.4.6.519\tools\OpenCover.Console.exe -target:"dotnet.exe" -targetargs:"test tests\SixLabors.Core.Tests\SixLabors.Core.Tests.csproj --no-build -c release" -searchdirs:"tests\SixLabors.Core.Tests\bin\Release\netcoreapp2.1" -register:user -output:.\SixLabors.Core.Coverage.xml -hideskipped:All -returntargetcode -oldStyle -filter:"+[SixLabors.*]*" 
 
 if %errorlevel% neq 0 exit /b %errorlevel%
 

tests/SixLabors.Core.Tests/SixLabors.Core.Tests.csproj

@@ -2,7 +2,7 @@
 
   <PropertyGroup>
     <VersionPrefix>0.0.0</VersionPrefix>
-    <TargetFrameworks>netcoreapp1.1;netcoreapp2.0;</TargetFrameworks>
+    <TargetFrameworks>netcoreapp1.1;netcoreapp2.1;</TargetFrameworks>
     <AssemblyName>SixLabors.Core.Tests</AssemblyName>
     <PackageId>SixLabors.Shapes.Tests</PackageId>
     <GenerateRuntimeConfigurationFiles>true</GenerateRuntimeConfigurationFiles>
@@ -38,8 +38,4 @@
     <ProjectReference Include="..\..\src\SixLabors.Core\SixLabors.Core.csproj" />
   </ItemGroup>
 
-  <ItemGroup>
-    <Service Include="{82a7f48d-3b50-4b1e-b82e-3ada8210c358}" />
-  </ItemGroup>
-
 </Project>