Updated Microsoft.CodeAnalysis package to 3.6.0 for CSharp8 tests

Author: vweijsters

StyleCop.Analyzers/StyleCop.Analyzers.Test.CSharp8/StyleCop.Analyzers.Test.CSharp8.csproj

@@ -17,7 +17,7 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.CodeAnalysis" Version="3.3.1-beta3-final" />
+    <PackageReference Include="Microsoft.CodeAnalysis" Version="3.6.0" />
     <PackageReference Include="xunit" Version="2.4.1" />
     <PackageReference Include="xunit.runner.visualstudio" Version="2.4.1" PrivateAssets="all" />
   </ItemGroup>