Latest alpha 042 doesn't seem to recognise net5.0

Description

6.0.0-alpha042 doesn't recognise net5.0 specification.

$  dotnet paket --version
Paket version 6.0.0-alpha042

$  dotnet --info
.NET SDK (reflecting any global.json):
 Version:   5.0.100-rc.1.20452.10
 Commit:    473d1b592e

Runtime Environment:
 OS Name:     ubuntu
 OS Version:  20.04
 OS Platform: Linux
 RID:         ubuntu.20.04-x64
 Base Path:   /snap/dotnet-sdk/100/sdk/5.0.100-rc.1.20452.10/

Host (useful for support):
  Version: 5.0.0-rc.1.20451.14
  Commit:  38017c3935

.NET SDKs installed:
  5.0.100-rc.1.20452.10 [/snap/dotnet-sdk/100/sdk]

.NET runtimes installed:
  Microsoft.AspNetCore.App 5.0.0-rc.1.20451.17 [/snap/dotnet-sdk/100/shared/Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 5.0.0-rc.1.20451.14 [/snap/dotnet-sdk/100/shared/Microsoft.NETCore.App]

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

Repro steps

Please provide the steps required to reproduce the problem

1. Step A

$  head paket.*
==> paket.dependencies <==
source https://api.nuget.org/v3/index.json
framework: net5.0
storage: none

nuget Fable.Remoting.Giraffe
nuget Saturn
nuget Expecto

nuget Fable.Core
nuget Fable.Elmish

==> paket.lock <==
STORAGE: NONE
RESTRICTION: == net5.0
NUGET
  remote: https://api.nuget.org/v3/index.json
    Expecto (9.0.2)
      FSharp.Core (>= 4.6)
      Mono.Cecil (>= 0.11.2)
    Fable.Browser.Blob (1.1)
      Fable.Core (>= 3.0)
      FSharp.Core (>= 4.6.2)

2. Step B

$ dotnet fake build --target run

Expected behavior

net5.0 specification recognised successfully, as per release notes

Actual behavior

$  dotnet fake build --target run
Performance:
 - Cli parsing: 237 milliseconds
 - Packages: 67 milliseconds
 - Script analyzing: 171 milliseconds
 - Runtime: 574 milliseconds
There was a problem while setting up the environment:
-> Error in paket.dependencies line 2
     Could not parse framework 'net5.0'. Try to update or install again or report a paket bug.
Hint: If you just upgraded the fake-runner you can try to remove the .fake directory and try again.

Known workarounds

None that I know of

Reproduce the parse failure using the framework: net5.0 entry in paket.dependencies and the dotnet fake build --target run command. Start by tracing Paket's framework parsing from that dependency declaration and compare it with the net5.0 release-note expectation. Done means the command accepts net5.0 without the framework parse error.