Log Message:
shells/nushell: update to 0.68.0

This is a huge jump over several releases and it's impossible to list changes.
Please visit https://www.nushell.sh/blog/ for the details of every release.

Be aware that there are lots of changes across all aspects of Nushell.

 - There's a new engine, new line editor, and new commands.
 - Configuration files will not work and have to be re-written.
 - Previous scripts will need to be updated, and you'll need to learn some of
   the new ways of doing things in Nushell to get back to the same level of
   comfort.
 - Several shell improvements and behavior changes.
 - There's also a new plugin architecture and quite a number of breaking
   changes after fixing design flaws, cleaned-up the design, and rethought how
   commands should work.
 - New additional startup file (env.nu) which, sets up the environment that
   you'll run Nushell in. As a result, you're able to set up important
   environment variables like $env.NU_LIB_DIRS before 'config.nu' begins to run.
 - Deeper integration with SQLite, new completion logic, introduction of
   overlays, hooks, lazy dataframes, input overloading, input/output type,
   new variable naming convention ...

So, please do read about the changes before.