docs: fix outdated urllib2 reference to urllib

[jlaportebot]

Summary

Fixed outdated documentation reference from urllib2 to urllib.

Changes

• Updated README.md line 130 to use urllib instead of urllib2
• Python 3 uses urllib module, not urllib2 (which was Python 2)

Why this matters

The documentation was referencing the Python 2 module urllib2, which doesn't exist in Python 3. This could confuse users trying to understand the HTTP client fallback behavior in Python 3 environments.

Testing

This is a documentation-only change with no code impact. The change accurately reflects the actual behavior of the library in Python 3 environments.

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[jlaportebot]

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[jlaportebot]

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