Get local/current version

[mjhymowitz]

Adding frum current command to get the ruby version running locally.
Instead of using frum versions to get all ruby versions installed and the local version.
frum current will return the active ruby version being used. If a version is set locally the local version is return else return global version.

[mjhymowitz]

This will likely reuse a lot of code from the src/commands/versions.rs file

[mjhymowitz]

nvm this looks like a lot more work than I first thought