[Docs] Consistent use of self-closing tags in layout

_layouts/default.html

@@ -6,12 +6,12 @@
   <meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1">
   <title>React | {{ page.title }}</title>
   <meta name="viewport" content="width=device-width">
-  <meta property="og:title" content="React | {{ page.title }}" />
-  <meta property="og:type" content="website" />
-  <meta property="og:url" content="http://facebook.github.io/react{{ page.url }}" />
-  <meta property="og:image" content="http://facebook.github.io/react/img/logo_og.png" />
-  <meta property="og:description" content="A JavaScript library for building user interfaces" />
-  <meta property="fb:app_id" content="623268441017527" />
+  <meta property="og:title" content="React | {{ page.title }}">
+  <meta property="og:type" content="website">
+  <meta property="og:url" content="http://facebook.github.io/react{{ page.url }}">
+  <meta property="og:image" content="http://facebook.github.io/react/img/logo_og.png">
+  <meta property="og:description" content="A JavaScript library for building user interfaces">
+  <meta property="fb:app_id" content="623268441017527">
 
   <link rel="shortcut icon" href="/react/favicon.ico">
   <link rel="alternate" type="application/rss+xml" title="{{ site.name }}" href="{{ site.url }}{{ site.baseurl }}/feed.xml">