C# build with netcore3.1 failed on Mac/OS and succed on Linux

I build for both Linux and Mac os , language c#

The build report of Mac os is here

and get the error:

$ wget --retry-connrefused --waitretry=1 -O /tmp/dotnet.pkg https://dotnetcli.azureedge.net/dotnet/Sdk/3.0/dotnet-sdk-3.0-osx-x64.pkg
–2020-03-28 09:31:31-- https://dotnetcli.azureedge.net/dotnet/Sdk/3.0/dotnet-sdk-3.0-osx-x64.pkg
Resolving dotnetcli.azureedge.net (dotnetcli.azureedge.net)…
Connecting to dotnetcli.azureedge.net (dotnetcli.azureedge.net)||:443… connected.
HTTP request sent, awaiting response… 404 Not Found

2020-03-28 09:31:31 ERROR 404: Not Found.

The command “wget --retry-connrefused --waitretry=1 -O /tmp/dotnet.pkg https://dotnetcli.azureedge.net/dotnet/Sdk/3.0/dotnet-sdk-3.0-osx-x64.pkg” failed and exited with 8 during .

Your build has been stopped.

The configuration file travis.yml is here

cc @joshua-anderson @akoeplinger

@Joshua-Anderson should probably use the official install scripts: dotnet-install scripts - .NET Core CLI | Microsoft Docs Judging by https://dotnet.microsoft.com/download/dotnet-core/3.1 and https://dotnet.microsoft.com/download/dotnet-core/3.0, they changed the downloads layout.

Thanks @native-api for reply.
I resolved the issue by modifying travis.yml and using the exact version of SDK:

dotnet: 3.1.200

instead of: dotnet: 3.1
The build report: here
The complete travis.yml here