我正在尝试通过dotnet-cli安装dotnet-ef工具。

我输入的命令：dotnet tool install --global dotnet-ef

我给我以下错误：

The tool package could not be restored.
Tool 'dotnet-ef' failed to install. This failure may have been caused by:

* You are attempting to install a preview release and did not use the --version option to specify the version.
* A package by this name was found,but it was not a .NET Core tool.
* The required NuGet feed cannot be accessed,perhaps because of an Internet connection problem.
* You mistyped the name of the tool.

我正在使用dotnet 3.0，我相信我在MacOS上没有这个问题，我现在正在尝试在Windows 10计算机上执行相同的命令，这给了我这个错误。

使用dotnet --info命令的一些信息：

.NET Core SDK (reflecting any global.json):
 Version:   3.0.100
 Commit:    04339c3a26

Runtime Environment:
 OS Name:     Windows
 OS Version:  10.0.18362
 OS Platform: Windows
 RID:         win10-x64
 Base Path:   C:\Program Files\dotnet\sdk\3.0.100\

Host (useful for support):
  Version: 3.0.0
  Commit:  7d57652f33

.NET Core SDKs installed:
  3.0.100 [C:\Program Files\dotnet\sdk]

.NET Core runtimes installed:
  microsoft.AspNetCore.All 2.1.13 [C:\Program Files\dotnet\shared\microsoft.AspNetCore.All]
  microsoft.AspNetCore.App 2.1.13 [C:\Program Files\dotnet\shared\microsoft.AspNetCore.App]
  microsoft.AspNetCore.App 3.0.0 [C:\Program Files\dotnet\shared\microsoft.AspNetCore.App]
  microsoft.NETCore.App 2.1.13 [C:\Program Files\dotnet\shared\microsoft.NETCore.App]
  microsoft.NETCore.App 3.0.0 [C:\Program Files\dotnet\shared\microsoft.NETCore.App]
  microsoft.WindowsDesktop.App 3.0.0 [C:\Program Files\dotnet\shared\microsoft.WindowsDesktop.App]

To install additional .NET Core runtimes or SDKs:
  https://aka.ms/dotnet-download