chore: add playground entry on homepage (#590)

Author: iChenLei

Diff for: .assemblerc.yml

@@ -88,15 +88,15 @@ description: >
 
 # URLs
 homepage:          http://lesscss.org
-onlineeditor:      http://lesscss.org/less-preview
+playground:      http://lesscss.org/less-preview
 repo:              <%= pkg.homepage %>
 issues:            <%= pkg.bugs.url %>?&state=open
 download:
   source:          <%= pkg.homepage %>/archive/master.zip
   latest:          https://raw.github.com/less/less.js/master/dist/less.js
 
 cdn:
-  cloudflare:      https://cdn.jsdelivr.net/npm/less@4
+  cloudflare:      https://cdn.jsdelivr.net/npm/less
 
 
 # =============================================

Diff for: templates/includes/docs-header.hbs

@@ -12,6 +12,8 @@
       <p>Or the browser:</p>
       <code>{{marked '<link rel="stylesheet/less" type="text/css" href="styles.less" />' }}</code><br>
       <code>&lt;script src="<a href="{{ site.cdn.cloudflare }}">{{ site.cdn.cloudflare }}</a>" &gt;&lt;/script&gt;</code><br>
+      <br><br>
+      <p>Or try <code><a href="{{ site.playground }}">online playground</a></code> ! 🆕</p>
 
     </div>
   </div>