message: Prepare changelog for v0.12.0-rc.4
diff: +Changes in [0.12.0-rc.4](https://github.com/matrix-org/matrix-react-sdk/releases/tag/v0.12.0-rc.4) (2018-03-22)
  +===============================================================================================================
  +[Full Changelog](https://github.com/matrix-org/matrix-react-sdk/compare/v0.12.0-rc.3...v0.12.0-rc.4)
  +
  + * Fix broken import preventing people tag
  + [\#1811](https://github.com/matrix-org/matrix-react-sdk/pull/1811)
  +
  Changes in [0.12.0-rc.3](https://github.com/matrix-org/matrix-react-sdk/releases/tag/v0.12.0-rc.3) (2018-03-20)
  ===============================================================================================================
  [Full Changelog](https://github.com/matrix-org/matrix-react-sdk/compare/v0.12.0-rc.2...v0.12.0-rc.3)
  