Fix: svg-net#746 'Error with duplicate ColorConverter.cs in Svg.dll a…

…nd .NET Standard 2.1' issue.

Source/Svg.csproj

@@ -1,6 +1,6 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;netcoreapp2.2;net452</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;netstandard2.1;netcoreapp2.2;net452</TargetFrameworks>
     <PackageLicenseExpression>MS-PL</PackageLicenseExpression>
     <RootNamespace>Svg</RootNamespace>
     <AssemblyName>Svg</AssemblyName>
@@ -63,12 +63,17 @@
     <Title>Svg for .Net Core 2.2</Title>
     <DefineConstants>$(DefineConstants);NETCORE;NETCORE22</DefineConstants>
   </PropertyGroup>
-  
+
   <PropertyGroup Condition="'$(TargetFramework)'=='netstandard2.0'">
     <Title>Svg for .Net Standard 2.0</Title>
     <DefineConstants>$(DefineConstants);NETSTANDARD;NETSTANDARD20</DefineConstants>
   </PropertyGroup>
-
+
+  <PropertyGroup Condition="'$(TargetFramework)'=='netstandard2.1'">
+    <Title>Svg for .Net Standard 2.1</Title>
+    <DefineConstants>$(DefineConstants);NETSTANDARD</DefineConstants>
+  </PropertyGroup>
+
   <ItemGroup Condition="'$(TargetFramework)'=='net452'">
     <Reference Include="System" />
     <Reference Include="System.Core" />
@@ -91,7 +96,7 @@
     </PackageReference>
   </ItemGroup>
 
-  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0'">
+  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0' Or '$(TargetFramework)' == 'netstandard2.1'">
     <PackageReference Include="System.Drawing.Common">
       <Version>4.7.0</Version>
     </PackageReference>
@@ -101,12 +106,11 @@
   </ItemGroup>
 
   <!-- Mac specific include -->
-  
+
   <ItemGroup Condition="'$(TargetFramework)' == 'netcoreapp2.2'">
     <PackageReference Include="runtime.osx.10.10-x64.CoreCompat.System.Drawing" Version="5.8.64" />
   </ItemGroup>
-
-
+
   <ItemGroup>
     <Compile Remove=".\External\ExCSS\Parser.generated.cs" />
     <Compile Remove=".\External\ExCSS\ParserX.cs" />