Improve grammar on changelog #10025 entry

Author: nhunzaker

CHANGELOG.md

@@ -8,7 +8,7 @@
 * Prevent event handlers from receiving extra argument (dev only) ([@aweary](https://github.com/aweary) in [#10115](https://github.com/facebook/react/pull/8363)
 * Fix cases where onChange would not fire with defaultChecked on radio inputs ([@jquense](https://github.com/jquense) in [#10156](https://github.com/facebook/react/pull/10156))
 * Add support for controlList attribute to DOM property whitelist ([@nhunzaker](https://github.com/nhunzaker) in [#9940](https://github.com/facebook/react/pull/9940))
-* Fix a bug where creating an element with ref in constructor threw an error in dev mode ([@iansu](https://github.com/iansu) in [#10025](https://github.com/facebook/react/pull/10025))
+* Fix a bug where creating an element with a ref in a constructor threw an error in dev mode ([@iansu](https://github.com/iansu) in [#10025](https://github.com/facebook/react/pull/10025))
 
 ## 15.6.1 (June 14, 2017)