fix scroll speed

Author: Gaohaoyang

_layouts/default.html

@@ -15,7 +15,7 @@
     <script src="{{ " /js/smooth-scroll.min.js " | prepend: site.baseurl }}" charset="utf-8"></script>
     <script type="text/javascript">
       smoothScroll.init({
-        speed: 400, // Integer. How fast to complete the scroll in milliseconds
+        speed: 500, // Integer. How fast to complete the scroll in milliseconds
         easing: 'easeInOutCubic', // Easing pattern to use
         offset: 20, // Integer. How far to offset the scrolling anchor location in pixels
       });