Update test project dependencies

Author: traf72

.gitignore

@@ -5,6 +5,7 @@ bin
 obj
 *.suo
 /.vs
+/.idea
 /ExcelReportGenerator.Samples/Database
 ~$*
 /Dotfuscated

ExcelReportGenerator.Tests/ExcelReportGenerator.Tests.csproj

@@ -1,32 +1,26 @@
-<Project Sdk="Microsoft.NET.Sdk">
+<Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>netcoreapp2.0</TargetFramework>
-
+    <TargetFramework>netcoreapp3.1</TargetFramework>
+    <LangVersion>8</LangVersion>
     <IsPackable>false</IsPackable>
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.Extensions.Configuration" Version="2.2.0" />
-    <PackageReference Include="Microsoft.Extensions.Configuration.FileExtensions" Version="2.2.0" />
-    <PackageReference Include="Microsoft.Extensions.Configuration.Json" Version="2.2.0" />
-    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="15.9.0" />
-    <PackageReference Include="NSubstitute" Version="3.1.0" />
-    <PackageReference Include="NUnit" Version="3.11.0" />
-    <PackageReference Include="NUnit3TestAdapter" Version="3.11.2" />
-    <PackageReference Include="System.Data.SqlClient" Version="4.6.0" />
+    <PackageReference Include="Microsoft.Extensions.Configuration" Version="3.1.3" />
+    <PackageReference Include="Microsoft.Extensions.Configuration.FileExtensions" Version="3.1.3" />
+    <PackageReference Include="Microsoft.Extensions.Configuration.Json" Version="3.1.3" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="16.2.0" />
+    <PackageReference Include="NSubstitute" Version="4.2.1" />
+    <PackageReference Include="NUnit" Version="3.12.0" />
+    <PackageReference Include="NUnit3TestAdapter" Version="3.16.1" />
+    <PackageReference Include="System.Data.SqlClient" Version="4.8.1" />
   </ItemGroup>
 
   <ItemGroup>
     <ProjectReference Include="..\ExcelReportGenerator\ExcelReportGenerator.csproj" />
   </ItemGroup>
 
-  <ItemGroup>
-    <Reference Include="System">
-      <HintPath>System</HintPath>
-    </Reference>
-  </ItemGroup>
-
   <ItemGroup>
     <None Update="appsettings.json">
       <CopyToOutputDirectory>Always</CopyToOutputDirectory>