Updated site constants to 16.3

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 = '16.2.0';
+const version = '16.3.0';
 const babelURL = '//unpkg.com/babel-standalone@6.26.0/babel.min.js';
 
 export {urlRoot, version, babelURL};