Enforce usage of TLS 1.2 when building Chocolatey package

[Daniel15]

Summary
Currently, the Chocolatey build is failing: #5416

Invoke-WebRequest : The request was aborted: Could not create SSL/TLS secure channel.
At C:\Jenkins\workspace\yarn-chocolatey\scripts\build-chocolatey.ps1:44 char:1
+ Invoke-WebRequest -Uri $url -OutFile $installer_file

Github appears to have started enforcing TLS 1.2 at some point: https://www.ssllabs.com/ssltest/analyze.html?d=github.com

However, PowerShell uses TLS 1.0 by default. This causes an error when loading from GitHub via Invoke-WebRequest:

PS C:\Users\danlo> Invoke-WebRequest -Uri https://github.com/
Invoke-WebRequest : The request was aborted: Could not create SSL/TLS secure channel.
At line:1 char:1
+ Invoke-WebRequest -Uri https://github.com/
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We need to enforce TLS 1.2 to make it work:

[System.Net.ServicePointManager]::SecurityProtocol = [System.Net.SecurityProtocolType]::Tls12;

Test plan
Downloading Yarn installer via Invoke-WebRequest was failing:

Invoke-WebRequest -Uri "https://github.com/yarnpkg/yarn/releases/download/v1.5.1/yarn-1.5.1.msi" -OutFile "c:\temp\yarn.msi"
Invoke-WebRequest : The request was aborted: Could not create SSL/TLS secure channel.
At line:1 char:1
+ Invoke-WebRequest -Uri "https://github.com/yarnpkg/yarn/releases/down ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : InvalidOperation: (System.Net.HttpWebRequest:HttpWebRequest) [Invoke-WebRequest], WebExcept
   ion
    + FullyQualifiedErrorId : WebCmdletWebResponseException,Microsoft.PowerShell.Commands.InvokeWebRequestCommand

Now it works!

[Daniel15]

This worked: https://build.dan.cx/job/yarn-chocolatey/39/console