update changelog description to include rename of singer.state.write_bookmark to singer.state.set_bookmark

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Co-authored-by: Ben Allred <ben.allred@qlik.com>

Author: leslievandemark

CHANGELOG.md

@@ -1,7 +1,9 @@
 # Changelog
 
 ## 6.6.0
-  * Export singer.state functions from singer [#190](https://github.com/singer-io/singer-python/pull/190)
+  * Export singer.state functions from singer
+  * Rename singer.state.write_bookmark to singer.state.set_bookmark
+  * [#190](https://github.com/singer-io/singer-python/pull/190)
 
 ## 6.5.0
   * Add `activate_versions` state functions [#188](https://github.com/singer-io/singer-python/pull/188)