message: Prepare changelog for v0.12.7
diff: +Changes in [0.12.7](https://github.com/matrix-org/matrix-react-sdk/releases/tag/v0.12.7) (2018-06-12)
  +=====================================================================================================
  +[Full Changelog](https://github.com/matrix-org/matrix-react-sdk/compare/v0.12.7-rc.1...v0.12.7)
  +
  + * No changes since rc.1
  +
  Changes in [0.12.7-rc.1](https://github.com/matrix-org/matrix-react-sdk/releases/tag/v0.12.7-rc.1) (2018-06-06)
  ===============================================================================================================
  [Full Changelog](https://github.com/matrix-org/matrix-react-sdk/compare/v0.12.6...v0.12.7-rc.1)
  