Grammar fix for 15.0 blog post

Since "This" is the subject and singular, "have" should be "has"

New wording explaining implementation details

Grammar fix for 15.0 blog post

Since "This" is the subject and singular, "have" should be "has"

Fix wording for 15.0 blog post

nitpicks

_posts/2016-04-07-react-v15.md

@@ -67,7 +67,7 @@ If you can’t use `npm` yet, we provide pre-built browser builds for your conve
 
 - #### Rendering `null` now uses comment nodes
 
-    We’ve also made use of these comment nodes to change what `null` renders to. Rendering to `null` was a feature we added in React 0.11 and was implemented by rendering `<noscript>` elements. By rendering to comment nodes now, there’s a chance some of your CSS will be targeting the wrong thing, specifically if you are making use of `:nth-child` selectors. This, along with the other changes mentioned above, have always been considered implementation details of how React targets the DOM. We believe they are safe changes to make without going through a release with warnings detailing the subtle differences as they are details that should not be depended upon. Additionally, we have seen that these changes have improved React performance for many typical applications.  
+    We’ve also made use of these comment nodes to change what `null` renders to. Rendering to `null` was a feature we added in React 0.11 and was implemented by rendering `<noscript>` elements. By rendering to comment nodes now, there’s a chance some of your CSS will be targeting the wrong thing, specifically if you are making use of `:nth-child` selectors. React’s use of the `<noscript>` tag has always been considered an implementation detail of how React targets the DOM. We believe they are safe changes to make without going through a release with warnings detailing the subtle differences as they are details that should not be depended upon. Additionally, we have seen that these changes have improved React performance for many typical applications.  
 
     <small>[@spicyj](https://github.com/spicyj) in [#5451](https://github.com/facebook/react/pull/5451)</small>