Run the last command as the root user

We often see an error when executing a command that requires the root user permission. For example, installing a npm package as global probably requires `sudo`:

$ npm install -g package-name

In order to sudo the previous command, usually we press the Arrow key, append `sudo` to the beginning of the command and run it again.

It turns out that there is an easier, shorter command:

$ sudo !!

Here `!!` references the last command.