Enable TLS 1.2 in build.ps1 (#58)

Progress on NuGet/NuGetGallery#5551

Author: joelverhagen

build.ps1

@@ -24,6 +24,10 @@ trap {
 if (-not (Test-Path "$PSScriptRoot/build")) {
     New-Item -Path "$PSScriptRoot/build" -ItemType "directory"
 }
+
+# Enable TLS 1.2 since GitHub requires it.
+[Net.ServicePointManager]::SecurityProtocol = [Net.ServicePointManager]::SecurityProtocol -bor [Net.SecurityProtocolType]::Tls12
+
 wget -UseBasicParsing -Uri "https://raw.githubusercontent.com/NuGet/ServerCommon/$BuildBranch/build/init.ps1" -OutFile "$PSScriptRoot/build/init.ps1"
 . "$PSScriptRoot/build/init.ps1" -BuildBranch "$BuildBranch"