Support FsCheck3 pre-release in pack fake target.

FsCheck3 project is packaged as a pre-release version of Expecto.FsCheck.
Setting "Version" in the CLI command overwrites the full version.
So, instead write VersionPrefix. Then the pack experience is uniform
across all packages and supports packing FsCheck3

build.fsx

@@ -117,7 +117,7 @@ Target.create "Pack" <| fun _ ->
         NoLogo = true
         DoRestore = false
         Properties = [
-          "Version", release.NugetVersion
+          "VersionPrefix", release.NugetVersion
           "PackageReleaseNotes", String.toLines release.Notes
         ]
     }