global.jsons target a specific .net core 3.1 SDK version, should target .net core 3.1 in general

[klimisa]

global.json currently targets a specific .net core 3.1 SDK version

FsCodec/global.json

Lines 1 to 5 in 0608f83

	{
	"sdk": {
	"version": "3.1.101"
	}
	}

As result when I try to build the project on my machine I get following error:

dotnet build
A compatible installed .NET Core SDK for global.json version [3.1.101] from [/home/klimisa/Personal/dev/jet/FsCodec/global.json] was not found
Install the [3.1.101] .NET Core SDK or update [/home/klimisa/Personal/dev/jet/FsCodec/global.json] with an installed .NET Core SDK:
  3.1.402 [/usr/share/dotnet/sdk]

Therefore, if you have only the latest version then you can't build or run any tests.

[klimisa]

Suggested fix is to change global.json to the following,

{
  "sdk": {
    "version": "3.1.101",
    "rollForward": "latestFeature"
  }
}