message: Prepare changelog for v0.12.9
diff: +Changes in [0.12.9](https://github.com/matrix-org/matrix-react-sdk/releases/tag/v0.12.9) (2018-07-09)
  +=====================================================================================================
  +[Full Changelog](https://github.com/matrix-org/matrix-react-sdk/compare/v0.12.9-rc.2...v0.12.9)
  +
  + * No changes since rc.1
  +
  Changes in [0.12.9-rc.2](https://github.com/matrix-org/matrix-react-sdk/releases/tag/v0.12.9-rc.2) (2018-07-06)
  ===============================================================================================================
  [Full Changelog](https://github.com/matrix-org/matrix-react-sdk/compare/v0.12.9-rc.1...v0.12.9-rc.2)
  