Fix typo at Recursion concept metadata

[lacf95]

Found a typo on the Recursion concept, this PR fixes it

[github-actions[bot]]

Thank you for contributing to exercism/elixir 💜 🎉. This is an automated PR comment 🤖 for the maintainers of this repository that helps with the PR review process. You can safely ignore it and wait for a maintainer to review your changes.

Based on the files changed in this PR, it would be good to pay attention to the following details when reviewing the PR:

• General steps

  • 🏆 Does this PR need to receive a label with a reputation modifier (x:size/{tiny,small,medium,large,massive})? (A medium reputation amount is awarded by default, see docs)

• Concept changed

  • 👤 Does the author of the PR need to be added as an author or contributor in <concept>/.meta/config.json (see docs)?
  • 📖 Does the concept introduction provide all necessary information to solve this exercise?

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Automated comment created by PR Commenter 🤖.

[angelikatyborska]

Thank you