This function is only applicable for Hacknet Servers (the upgraded version of a Hacknet Node).
Spend the hashes generated by your Hacknet Servers on an upgrade. Returns a boolean value - true if the upgrade is successfully purchased, and false otherwise.
The name of the upgrade must be an exact match. The `upgTarget` argument is used for upgrades such as `Reduce Minimum Security`<!-- -->, which applies to a specific server. In this case, the `upgTarget` argument must be the hostname of the server.