message: Prepare changelog for v0.12.8-rc.2
diff: +Changes in [0.12.8-rc.2](https://github.com/matrix-org/matrix-react-sdk/releases/tag/v0.12.8-rc.2) (2018-06-22)
  +===============================================================================================================
  +[Full Changelog](https://github.com/matrix-org/matrix-react-sdk/compare/v0.12.8-rc.1...v0.12.8-rc.2)
  +
  + * slash got consumed in the consolidation
  + [\#1998](https://github.com/matrix-org/matrix-react-sdk/pull/1998)
  +
  Changes in [0.12.8-rc.1](https://github.com/matrix-org/matrix-react-sdk/releases/tag/v0.12.8-rc.1) (2018-06-21)
  ===============================================================================================================
  [Full Changelog](https://github.com/matrix-org/matrix-react-sdk/compare/v0.12.7...v0.12.8-rc.1)
  