为什么我不能在Heroku上发布Asp.Net Core应用程序？

Question

发布时出现以下错误：

  

找不到指定的框架'Microsoft.NETCore.App'版本'2.0.9'。   远程：-找到以下框架：   远程：3.0.0，位于[/app/tmp/cache/dotnet/3.0.100/sdk/shared/Microsoft.NETCore.App]   My.csproj文件：

    <Project Sdk="Microsoft.NET.Sdk.Web">
  <PropertyGroup>
    <TargetFramework>netcoreapp2.2</TargetFramework>
    <AspNetCoreHostingModel>InProcess</AspNetCoreHostingModel>
  </PropertyGroup>


  <ItemGroup>
    <PackageReference Include="Microsoft.AspNetCore.App" />
    <PackageReference Include="Microsoft.AspNetCore.Razor.Design" Version="2.2.0" PrivateAssets="All" />
    <PackageReference Include="Microsoft.VisualStudio.Web.CodeGeneration.Design" Version="2.2.4" />
  </ItemGroup>


  <ItemGroup>
    <Reference Include="M2Mqtt.Net">
      <HintPath>M2Mqtt.Net.dll</HintPath>
    </Reference>
  </ItemGroup>


  <ItemGroup>
    <PackageReference Update="Microsoft.NETCore.App" Version="2.2.8" />
  </ItemGroup>


  <ProjectExtensions><VisualStudio><UserProperties properties_4launchsettings_1json__JsonSchema="" /></VisualStudio></ProjectExtensions>

</Project>