Prepare changelog for v0.13.0-rc.2

CHANGELOG.md

+Changes in [0.13.0-rc.2](https://github.com/matrix-org/matrix-react-sdk/releases/tag/v0.13.0-rc.2) (2018-07-24)
+===============================================================================================================
+[Full Changelog](https://github.com/matrix-org/matrix-react-sdk/compare/v0.13.0-rc.1...v0.13.0-rc.2)
+
+ * Take jitsi conf calling out of labs
+   [\#2087](https://github.com/matrix-org/matrix-react-sdk/pull/2087)
+
 Changes in [0.13.0-rc.1](https://github.com/matrix-org/matrix-react-sdk/releases/tag/v0.13.0-rc.1) (2018-07-24)
 ===============================================================================================================
 [Full Changelog](https://github.com/matrix-org/matrix-react-sdk/compare/v0.12.9...v0.13.0-rc.1)