Updated other packages.

src/Discord.Net.Core/Discord.Net.Core.csproj

@@ -11,9 +11,11 @@
   </PropertyGroup>
   <ItemGroup>
     <PackageReference Include="Newtonsoft.Json" Version="12.0.3" />
-    <PackageReference Include="System.Collections.Immutable" Version="1.7.1" />
-    <PackageReference Include="System.Interactive.Async" Version="4.1.1" />
-    <PackageReference Include="IDisposableAnalyzers" Version="3.4.3">
+    <!-- oddly enough supports .NET Core 2.1+ and other frameworks. -->
+    <PackageReference Include="System.Collections.Immutable" Version="5.0.0" />
+    <!-- <PackageReference Include="System.Interactive.Async" Version="5.0.0" /> -->
+    <PackageReference Include="Microsoft.Bcl.AsyncInterfaces" Version="5.0.0" />
+    <PackageReference Include="IDisposableAnalyzers" Version="3.4.8">
       <PrivateAssets>all</PrivateAssets>
     </PackageReference>
   </ItemGroup>