Log Message:
Update to 3.1.5. From the changelog:

- Add a more specific error message if `git` is not installed.
- Allow for using `mob timer` outside of git repositories.
- Fix: `mob done --squash-wip` now successfully auto-merges
  auto-mergeable diverging changes.
- Print the help output whenever any kind of help argument (`help`,
  `--help`, `-h`) is present in the command, e.g. `mob s 10 -h`.
- Adds a warning to `mob start` in case the wip branch diverges from the
  main branch.
- Various fixes in suggestion of next typist:
  - Show list of last committers only if there are any.
  - Skip suggestions if there has only been a single person so far.
  - Consider the case of a new typist joining the session.
  - Fix reporting on first commit.
- Show a deprecation warning when MOB_DONE_SQUASH is set to `true` or
  `false` in the environment variable or in the .mob configuration file.