feat(providers): detect VERCEL and VERCEL_ENV

[nozomuikuta]

🔗 Linked issue

Resolves #54.

❓ Type of change

• 📖 Documentation (updates to the documentation, readme, or JSdoc annotations)
• 🐞 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)
• 🧹 Chore (updates to the build process or auxiliary tools and libraries)
• ⚠️ 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.
  • not applicable

[codecov]

Codecov Report

Merging #58 (4899dd7) into main (53ccaba) will increase coverage by 0.07%.
Report is 7 commits behind head on main.
The diff coverage is 100.00%.

❗ Current head 4899dd7 differs from pull request most recent head 9bf8f58. Consider uploading reports for the commit 9bf8f58 to get more accurate results

@@            Coverage Diff             @@
##             main      #58      +/-   ##
==========================================
+ Coverage   92.93%   93.01%   +0.07%     
==========================================
  Files           2        2              
  Lines         184      186       +2     
  Branches       14       14              
==========================================
+ Hits          171      173       +2     
  Misses         13       13              

Files Changed	Coverage Δ
src/providers.ts	89.92% <100.00%> (+0.15%)	⬆️

[pi0]

Thanks!