fix: fix typo

Author: kt3k

source/layout/index.njk

@@ -11,7 +11,7 @@
 
 <ul>
   <li><a href="https://nodejs.org/api/">Node.js 最新</a>
-  <li><a href="https://nodejs.org/dist/latest-v8.x/docs/api/">Node.js v6.x</a>
+  <li><a href="https://nodejs.org/dist/latest-v8.x/docs/api/">Node.js v8.x</a>
   <li><a href="https://nodejs.org/dist/latest-v6.x/docs/api/">Node.js v6.x</a>
   <li><a href="https://nodejs.org/dist/latest-v4.x/docs/api/">Node.js v4.x</a>
 </ul>