doc: update logger link in readme

[glebpigulevsky]

Requirements

• [ ] I have added test coverage for new or changed functionality
• [x] I have followed the repository's pull request submission guidelines
• [x] I have validated my changes against all supported platform versions

Related issues

https://github.com/launchdarkly/js-client-sdk/issues/293 fix for last point for obsolete documentation link

Describe the solution you've provided

update outdated link

[kinyoklion]

Thank you for the contribution!