Fix tag usage display on admin dashboard

app/views/admin/dashboard/index.html.haml

@@ -146,4 +146,4 @@
         - @trending_hashtags.each do |tag|
           %li
             = link_to "##{tag.name}", web_url("timelines/tag/#{tag.name}")
-            %span.pull-right= number_with_delimiter(tag.history[0]['accounts'].to_i)
+            %span.pull-right= number_with_delimiter(tag.history[0][:accounts].to_i)