Fix style= formatting in v15 rc blog post

(cherry picked from commit 8c57fd9)

Author: zpao

docs/_posts/2016-03-07-react-v15-rc1.md

@@ -79,7 +79,7 @@ Each of these changes will continue to work as before with a new warning until t
 ### New helpful warnings
 
 - If you use a minified copy of the _development_ build, React DOM kindly encourages you to use the faster production build instead.
-- React DOM: When specifying a unit-less CSS value as a string, a future version will not add `px` automatically. This version now warns in this case (ex: writing `style={{width: '300'}}`. (Unitless *number* values like `width: 300` are unchanged.)
+- React DOM: When specifying a unit-less CSS value as a string, a future version will not add `px` automatically. This version now warns in this case (ex: writing `style={{'{{'}}width: '300'}}`. (Unitless *number* values like `width: 300` are unchanged.)
 - Synthetic Events will now warn when setting and accessing properties (which will not get cleared appropriately), as well as warn on access after an event has been returned to the pool.
 - Elements will now warn when attempting to read `ref` and `key` from the props.
 - React DOM now attempts to warn for mistyped event handlers on DOM elements (ex: `onclick` which should be `onClick`)