Add PR facebook#9584 to 15.6 change log

Updating the change log~ :)

**issue:**
facebook#9398

Author: flarnie

CHANGELOG.md

@@ -4,6 +4,7 @@
 
 ### React
 
+* Fix bug where controlled number input mistakenly allowed period.  ([@nhunzaker](https://github.com/nhunzaker) in [#9584](https://github.com/facebook/react/pull/9584))
 * Fix bug where performance entries were being cleared.  ([@chrisui](https://github.com/chrisui) in [#9451](https://github.com/facebook/react/pull/9451))
 * Stop adding 'px' to numbers passed for unitless CSS Grid attributes.  ([@ericsakmar](https://github.com/ericsakmar) in [#9185](https://github.com/facebook/react/pull/9185))
 * Deprecate `React.createMixin` helper, which was never used. ([@aweary](https://github.com/aweary) in [#8853](https://github.com/facebook/react/pull/8853))