Prepare changelog for v0.13.3

Author: dbkr

CHANGELOG.md

@@ -1,3 +1,9 @@
+Changes in [0.13.3](https://github.com/matrix-org/matrix-react-sdk/releases/tag/v0.13.3) (2018-09-03)
+=====================================================================================================
+[Full Changelog](https://github.com/matrix-org/matrix-react-sdk/compare/v0.13.3-rc.2...v0.13.3)
+
+ * No changes since rc.2
+
 Changes in [0.13.3-rc.2](https://github.com/matrix-org/matrix-react-sdk/releases/tag/v0.13.3-rc.2) (2018-08-31)
 ===============================================================================================================
 [Full Changelog](https://github.com/matrix-org/matrix-react-sdk/compare/v0.13.3-rc.1...v0.13.3-rc.2)