Command to upgrade pinned node platforms for default tools

[charlespierce]

Since we pin the version of Node to use for each tool, those versions will eventually get out-of-date and need to be updated. Currently, the only way to do that is to run:

$ volta uninstall <package>
$ volta install <package>

For each package. We should have a command that allows users to update all of their tools to the most recent LTS Node.