Update CHANGELOG.md (#16439)

* Update CHANGELOG.md

Fixed typo

Author: bbolek

packages/react-devtools/CHANGELOG.md

@@ -20,7 +20,7 @@
 
 ## 4.0.3 (August 17, 2019)
 #### Bug fixes
-* ES6 `Map` and `Set`, typed arrays, and other unnserializable types (e.g. Immutable JS) can now be inspected.
+* ES6 `Map` and `Set`, typed arrays, and other unserializable types (e.g. Immutable JS) can now be inspected.
 * Empty objects and arrays now display an "(empty)" label to the right to reduce confusion.
 * Components that use only the `useContext` hook now properly display hooks values in side panel.
 * Style editor now supports single quotes around string values (e.g. both `"red"` and `'red'`).