Update Changelog.md

JonRowe · web-flow · commit 18beef8960cd · 2021-04-29T09:03:20.000+01:00
diff --git a/Changelog.md b/Changelog.md
@@ -1,7 +1,9 @@
 ### Development
 
 Bug Fixes:
-* Fix reentrant mutex for Ruby 3.0. (Benoit Daloze, #504)
+
+* Use `Mutex#owned?` to allow `RSpec::Support::ReentrantMutex` to work in
+  nested Fibers on Ruby 3.0 and later. (Benoit Daloze, #503, #504)
 
 ### 3.10.2 / 2021-01-28
 [Full Changelog](http://github.com/rspec/rspec-support/compare/v3.10.1...v3.10.2)
