message: Prepare changelog for v0.8.7-rc.3
diff: +Changes in [0.8.7-rc.3](https://github.com/matrix-org/matrix-react-sdk/releases/tag/v0.8.7-rc.3) (2017-04-10)
  +=============================================================================================================
  +[Full Changelog](https://github.com/matrix-org/matrix-react-sdk/compare/v0.8.7-rc.2...v0.8.7-rc.3)
  +
  + * Use matrix-js-sdk v0.7.6-rc.2
  +
  +
  Changes in [0.8.7-rc.2](https://github.com/matrix-org/matrix-react-sdk/releases/tag/v0.8.7-rc.2) (2017-04-10)
  =============================================================================================================
  [Full Changelog](https://github.com/matrix-org/matrix-react-sdk/compare/v0.8.7-rc.1...v0.8.7-rc.2)
  