Update the dotnet SDK install script URL in build.psm1 (#10927)

build.psm1

@@ -1569,7 +1569,7 @@ function Install-Dotnet {
     # Note that when it is null, Invoke-Expression (but not &) must be used to interpolate properly
     $sudo = if (!$NoSudo) { "sudo" }
 
-    $installObtainUrl = "https://dot.net/v1"
+    $installObtainUrl = "https://dotnet.microsoft.com/download/dotnet-core/scripts/v1"
     $uninstallObtainUrl = "https://raw.githubusercontent.com/dotnet/cli/master/scripts/obtain"
 
     # Install for Linux and OS X