Prepare changelog for v3.10.0

Author: RiotRobot

CHANGELOG.md

@@ -1,3 +1,9 @@
+Changes in [3.10.0](https://github.com/matrix-org/matrix-react-sdk/releases/tag/v3.10.0) (2020-12-07)
+=====================================================================================================
+[Full Changelog](https://github.com/matrix-org/matrix-react-sdk/compare/v3.10.0-rc.1...v3.10.0)
+
+ * Upgrade to JS SDK 9.3.0
+
 Changes in [3.10.0-rc.1](https://github.com/matrix-org/matrix-react-sdk/releases/tag/v3.10.0-rc.1) (2020-12-02)
 ===============================================================================================================
 [Full Changelog](https://github.com/matrix-org/matrix-react-sdk/compare/v3.9.0...v3.10.0-rc.1)