Fix typo in evaluate_solution_howto.md

[bshi]

Alternative solution is referenced as /tmp/solution-alt.json and then referenced again as /tmp/response-alt.json

Thank you for opening a Pull Request!

---

Before submitting your PR, there are a few things you can do to make sure it goes smoothly:

• Make sure to open a GitHub issue as a bug/feature request before writing your code! That way we can discuss the change, evaluate designs, and agree on the general idea
• Ensure the tests and linter pass
• Code coverage does not decrease (if any source code was changed)
• Appropriate docs were updated (if necessary)

Fixes #<issue_number_goes_here> 🦕

[ondrasej]

Thanks for catching this!