A must have for your script file to ease spreading a small proof of concept with dependencies!

PaketDependencyManagementMadeEasy.fsx

open System
open System.IO
open System.Diagnostics

let downloadDependencies deps =
    Environment.CurrentDirectory <- __SOURCE_DIRECTORY__

    if not (File.Exists "paket.exe") then
        async {
            let url = "http://fsprojects.github.io/Paket/stable"
            use wc = new Net.WebClient()
            wc.DownloadProgressChanged.Add(fun a -> printfn "Progress downloading paket.exe: %d" a.ProgressPercentage)
            let tmp = Path.GetTempFileName()
            let stable = wc.DownloadString(url) 
            do! wc.AsyncDownloadFile(stable |> Uri, tmp)
            File.Move(tmp,Path.GetFileName stable)
        } |> Async.RunSynchronously
        printfn "Finished downloading paket.exe!"

    let invokePaket args =
        use process = 
            new Process(
                StartInfo = 
                    new ProcessStartInfo(
                        FileName = "./paket.exe",
                        Arguments = args,
                        UseShellExecute = false))
        process.Start() |> ignore
        process.WaitForExit()
    if not (File.Exists "paket.dependencies") && not (File.Exists "paket.lock") then
        invokePaket "init"
    for dep in deps do
        sprintf "add %s" dep
        |> invokePaket
downloadDependencies [ "MathNet.Numerics"; "MathNet.Numerics.FSharp"] // Append the package names to this list! 

@amieres that's not about paket. GitHub has disabled TLS <= 1.2 How to enable TLS 1.2.

@Zagrophyte

Might want to add:
System.Net.ServicePointManager.SecurityProtocol <- System.Net.SecurityProtocolType.Tls12 // Github uses TLS 1.2
to the top of the file after open statements.

You are right! That did the trick.
Thank you!