Fix facebook open graph tags

Author: cvle

docs/media/preview.png

@@ -5,7 +5,7 @@
   <title>React CSS Transition · Take Control of your CSS Transitions</title>
   <meta property="og:title" content="React CSS Transition" />
   <meta property="og:description" content="Take Control of your CSS Transitions" />
-  <meta property="og:url" content="https://wikiwi.github.io/react-css-transition" />
+  <meta property="og:url" content="https://wikiwi.github.io/react-css-transition/" />
   <meta property="og:image" content="https://wikiwi.github.io/react-css-transition/preview.png" />
   <meta http-equiv="Content-type" content="text/html; charset=utf-8" />
   <meta name="viewport" content="width=device-width" />