Use absoluteURL instead of relativeURL for next/prev links (#783)

* Remove trailing slash for docs url

* undo remove trailing slash & use absoluteURL for next/prev links

* use baseUrl instead of hardcoded slash

lib/core/DocsLayout.js

@@ -13,16 +13,20 @@ const OnPageNav = require('./nav/OnPageNav.js');
 const Site = require('./Site.js');
 const translation = require('../server/translation.js');
 const path = require('path');
+const url = require('url');
 
 // component used to generate whole webpage for docs, including sidebar/header/footer
 class DocsLayout extends React.Component {
   getRelativeURL = (from, to) => {
     const extension = this.props.config.cleanUrl ? '' : '.html';
-    return (
+    const relativeHref =
       path
         .relative(from, to)
         .replace('\\', '/')
-        .replace(/^\.\.\//, '') + extension
+        .replace(/^\.\.\//, '') + extension;
+    return url.resolve(
+      `${this.props.config.baseUrl}${this.props.metadata.permalink}`,
+      relativeHref
     );
   };