Fix fish completion

[soraxas]

The fish completion for environments completion is currently broken.

That's due to some changes to micromamba's output.

I've tested that in previous micromamba version:

$ ./bin/micromamba --version
1.2.0

$ ./bin/micromamba env list

                                           __
          __  ______ ___  ____ _____ ___  / /_  ____ _
         / / / / __ `__ \/ __ `/ __ `__ \/ __ \/ __ `/
        / /_/ / / / / / / /_/ / / / / / / /_/ / /_/ /
       / .___/_/ /_/ /_/\__,_/_/ /_/ /_/_.___/\__,_/
      /_/

  Name     Active  Path                             
──────────────────────────────────────────────────────
  base             /home/soraxas/micromamba             
  my_other_env     /home/soraxas/micromamba/envs/octomap
...

Current latest version:

$ micromamba --version
1.4.6

$ micromamba env list
  Name     Active  Path                             
──────────────────────────────────────────────────────
  base             /home/soraxas/micromamba             
  my_other_env     /home/soraxas/micromamba/envs/octomap
...

Notice the missing $\mu$-mamba logo

---

We can fix the completion by changing the tail argument from 11 to 2, but I opt to a more "robust" approach using sed that currently works in both case.

But this is based on the assumption that

1. base environment always exists, and
2. base environment is always the first environment.

Are these assumption always correct?

[jonashaag]

Thanks for the fix! Unfortunately both assumptions are incorrect I think