Working directory fix for googletest submodule update (#2151)

* Working directory fix for submodule update

The git submodule update for googletest must be run from the script's root directory

* Added try-finally block around Push-Location

Great recommendation from @vors! 

The edit is a best practice incase the user Ctrl-C's out of the script. 

Tested locally by exiting out of: 
try { Push-Location C:\Users\; Start-Sleep -Seconds 60 } finally { Pop-Location }

build.psm1

@@ -698,9 +698,14 @@ function Start-PSBootstrap {
     try {
         # Update googletest submodule for linux native cmake
         if ($IsLinux -or $IsOSX) {
-            $Submodule = "$PSScriptRoot/src/libpsl-native/test/googletest"
-            Remove-Item -Path $Submodule -Recurse -Force -ErrorAction SilentlyContinue
-            git submodule update --init -- $submodule
+            try {
+                Push-Location $PSScriptRoot
+                $Submodule = "$PSScriptRoot/src/libpsl-native/test/googletest"
+                Remove-Item -Path $Submodule -Recurse -Force -ErrorAction SilentlyContinue
+                git submodule update --init -- $submodule
+            } finally {
+                Pop-Location
+            }
         }
 
         # Install ours and .NET's dependencies