docs: fix heroku typo

[clew-bot]

Typo on the Heroku providers section

Here is the link to the page: https://nitro.unjs.io/deploy/providers/heroku

🔗 Linked issue

❓ Type of change

• 📖 Documentation (updates to the documentation or readme)
• 🐞 Bug fix (a non-breaking change that fixes an issue)
• 👌 Enhancement (improving an existing functionality like performance)
• ✨ New feature (a non-breaking change that adds functionality)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

📝 Checklist

• I have linked an issue or discussion.
• I have updated the documentation accordingly.

[manniL]

Thanks!

[codecov]

Codecov Report

Merging #900 (97234bb) into main (f7eed65) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #900   +/-   ##
=======================================
  Coverage   67.50%   67.50%           
=======================================
  Files          59       59           
  Lines        5866     5866           
  Branches      637      637           
=======================================
  Hits         3960     3960           
  Misses       1897     1897           
  Partials        9        9           

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