Fix double slash in canonical URL

Author: Daniel15

site/jekyll/_layouts/default.html

@@ -8,7 +8,7 @@
   <meta name="viewport" content="width=device-width" />
   <meta property="og:title" content="{{ page.title }} | {{ site.name }}" />
   <meta property="og:type" content="website" />
-  <meta property="og:url" content="http://reactjs.net/{{ page.url }}" />
+  <meta property="og:url" content="http://reactjs.net{{ page.url }}" />
   <meta property="og:image" content="http://facebook.github.io/react/img/logo_og.png" />
   <meta property="og:description" content=".NET integration for ReactJS" />
   <meta property="fb:app_id" content="1417169611875552" />