fix 404 page (#321)

Author: Arhell

404.html

@@ -6,7 +6,7 @@
 permalink: /404.html
 ---
 
-<div class="not-found-page">
+<div class="not-found-page" style="height: 100%">
     <div class="container container--short">
         <h2>{{ site.data.languages[page.language]['404-title'] }}</h2>
         <p>{{ site.data.languages[page.language]['404-about'] }}</p>