Match changelog to ios

The change is the same so makes sense to have the same wording

Author: rlazo

firebase-ai/CHANGELOG.md

@@ -1,5 +1,6 @@
 # Unreleased
-* [feature] Added support for thoughts and thinking signatures.
+* [feature] Added support for returning thought summaries, which are synthesized
+  versions of a model's internal reasoning process.
 * [changed] Added better description for requests which fail due to the Gemini API not being
   configured.
 * [changed] Added a `dilation` parameter to `ImagenMaskReference.generateMaskAndPadForOutpainting`