Merge pull request #41 from coneybeare/master

Merge pull request 41

Author: alfredxing

lib/jekyll-archives/archive.rb

@@ -34,8 +34,8 @@ def initialize(site, title, type, posts)
         @config = site.config['jekyll-archives']
 
         # Generate slug if tag or category (taken from jekyll/jekyll/features/support/env.rb)
-        if title.is_a? String
-          @slug = Utils.slugify(title)
+        if title.to_s.length
+          @slug = Utils.slugify(title.to_s)
         end
 
         # Use ".html" for file extension and url for path