Add support for net46

Author: Zyano

src/AngleSharp.Io/AngleSharp.Io.csproj

@@ -1,8 +1,8 @@
-<Project Sdk="Microsoft.NET.Sdk">
+<Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <AssemblyName>AngleSharp.Io</AssemblyName>
     <RootNamespace>AngleSharp.Io</RootNamespace>
-    <TargetFrameworks Condition=" '$(OS)' == 'Windows_NT' ">netstandard2.0</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;net46</TargetFrameworks>
     <SignAssembly>true</SignAssembly>
     <AssemblyOriginatorKeyFile>Key.snk</AssemblyOriginatorKeyFile>
     <GenerateDocumentationFile>true</GenerateDocumentationFile>
@@ -11,6 +11,11 @@
 
   <ItemGroup>
     <PackageReference Include="AngleSharp" Version="0.13.0" />
+    <PackageReference Include="System.Net.WebSockets.Client" Version="4.3.2" />
+  </ItemGroup>
+  <ItemGroup Condition="'$(TargetFramework)' == 'net46'">
+    <Reference Include="System.Net" />
+    <Reference Include="System.Net.Http" />
   </ItemGroup>
 
   <PropertyGroup Condition=" '$(OS)' == 'Windows_NT' ">