Update version number in header and versions page (reactjs#71)

Author: reactjs-translation-bot

content/versions.yml

@@ -1,3 +1,5 @@
+- title: '16.8'
+  changelog: https://github.com/facebook/react/blob/master/CHANGELOG.md#1680-february-6-2019
 - title: '16.7'
   path: /version/16.7
   changelog: https://github.com/facebook/react/blob/master/CHANGELOG.md#1670-december-19-2018

src/site-constants.js

@@ -8,7 +8,7 @@
 // NOTE: We can't just use `location.toString()` because when we are rendering
 // the SSR part in node.js we won't have a proper location.
 const urlRoot = 'https://reactjs.org';
-const version = '16.7.0';
+const version = '16.8.0';
 const babelURL = 'https://unpkg.com/[email protected]/babel.min.js';
 
 export {urlRoot, version, babelURL};