Fix release Github link on website for latest RC version

Summary:
Each RC created ends with `rc.0` so the link on the website is broken. This PR fix this.

https://facebook.github.io/react-native/versions.html

But maybe it's the RC tag that is wrong and should be fixed instead of the website link.
Closes https://github.com/facebook/react-native/pull/9857

Differential Revision: D3852046

fbshipit-source-id: 122feaf81396c492c558eefe657915127eee7ffe

website/src/react-native/versions.js

@@ -36,7 +36,7 @@ var versions = React.createClass({
       return {
         title: title,
         path: isLatest ? '/react-native' : '/react-native/releases/' + version,
-        release: 'https://github.com/facebook/react-native/releases/tag/v' + version + '.0' + (isRC ? '-rc' : '')
+        release: 'https://github.com/facebook/react-native/releases/tag/v' + version + '.0' + (isRC ? '-rc.0' : '')
       }
     }));