message: Prepare changelog for v0.13.4
diff: +Changes in [0.13.4](https://github.com/matrix-org/matrix-react-sdk/releases/tag/v0.13.4) (2018-09-10)
  +=====================================================================================================
  +[Full Changelog](https://github.com/matrix-org/matrix-react-sdk/compare/v0.13.4-rc.1...v0.13.4)
  +
  + * No changes since rc.1
  +
  Changes in [0.13.4-rc.1](https://github.com/matrix-org/matrix-react-sdk/releases/tag/v0.13.4-rc.1) (2018-09-07)
  ===============================================================================================================
  [Full Changelog](https://github.com/matrix-org/matrix-react-sdk/compare/v0.13.3...v0.13.4-rc.1)
  