chore(changelog): add link for Python 3.8 EOL change (#249)

Signed-off-by: Yurii Serhiichuk <[email protected]>

Author: xSAVIKx

CHANGELOG.md

@@ -10,7 +10,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Changed
 
-- Dropped Python3.8 support while it has reached EOL. ([])
+- Dropped Python3.8 support while it has reached EOL. ([#249])
 
 ## [1.11.1]
 
@@ -301,3 +301,4 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 [#236]: https://github.com/cloudevents/sdk-python/pull/236
 [#240]: https://github.com/cloudevents/sdk-python/pull/240
 [#248]: https://github.com/cloudevents/sdk-python/pull/248
+[#249]: https://github.com/cloudevents/sdk-python/pull/249