Update script can fail if interrupted

[ocdtrekkie]

If during the preferred update flow, ExtractToDirectory creates the temp directory, but the update is interrupted prior to the batch file deleting the temp directory, future attempts to update will cause a crash. ExtractToDirectory has a handy "overwriteFiles" capability starting in .NET Core 2 which would elegantly dodge this possibility, but it's not available to us here yet.

[ocdtrekkie]

3ae4906 makes it a lot less likely someone will interrupt the updater, as the script is hidden when executing.