docs: update CHANGELOG.md

Author: karel-rehor

CHANGELOG.md

@@ -3,6 +3,8 @@
 ### Features
 
 - [#404](https://github.com/influxdata/influxdb-client-go/pull/404) Expose HTTP response headers in the Error type to aid analysis and debugging of error results.  Add selected response headers to the error log.
+  
+ Also, unified errors returned by WriteAPI, which now always returns `http.Error`    
 
 ### Fixes
 - [#403](https://github.com/influxdata/influxdb-client-go/pull/403) Custom checks de/serialization to allow calling server Check API