Update System.Linq.Async.csproj

Ix.NET/Source/System.Linq.Async/System.Linq.Async.csproj

@@ -24,7 +24,7 @@
   </ItemGroup>
 
   <ItemGroup>
-    <PackageReference Condition="'$(TargetFramework)' != 'netcoreapp3.0' and '$(TargetFramework)' != 'netstandard2.1' " Include="Microsoft.Bcl.AsyncInterfaces" Version="1.0.0-preview7.19314.2" />
+    <PackageReference Condition="'$(TargetFramework)' != 'netcoreapp3.0' and '$(TargetFramework)' != 'netstandard2.1' " Include="Microsoft.Bcl.AsyncInterfaces" Version="1.0.0-preview6.19303.8" />
     <ReferenceAssemblyProjectReference Include="..\refs\System.Linq.Async.Ref\System.Linq.Async.Ref.csproj" />
   </ItemGroup>