Fix \bbox problem with padding values that are decimals. (mathjax/MathJax#3568)

[dpvc]

This PR fixes a problem with \bbox where padding values that are decimals can lead to NaN values. This was caused by using parseInt() instead of parseFloat(), so the fix is easy.

Resolves issue mathjax/MathJax#3568.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.47%. Comparing base (a65456c) to head (e69ef94).

Additional details and impacted files

@@            Coverage Diff             @@
##           develop    #1503     +/-   ##
==========================================
  Coverage    86.47%   86.47%             
==========================================
  Files          340      340             
  Lines        86125    86125             
  Branches      3206     4848   +1642     
==========================================
  Hits         74476    74476             
+ Misses       11649    11628     -21     
- Partials         0       21     +21     

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.