message: Prepare changelog for v0.8.8-rc.1
diff: +Changes in [0.8.8-rc.1](https://github.com/matrix-org/matrix-react-sdk/releases/tag/v0.8.8-rc.1) (2017-04-21)
  +=============================================================================================================
  +[Full Changelog](https://github.com/matrix-org/matrix-react-sdk/compare/v0.8.7...v0.8.8-rc.1)
  +
  + * Update js-sdk to fix registration without a captcha (https://github.com/vector-im/riot-web/issues/3621)
  +
  +
  Changes in [0.8.7](https://github.com/matrix-org/matrix-react-sdk/releases/tag/v0.8.7) (2017-04-12)
  ===================================================================================================
  [Full Changelog](https://github.com/matrix-org/matrix-react-sdk/compare/v0.8.7-rc.4...v0.8.7)
  