Always return a String for the Total header

Rack seems to expect that header values will always be a String, and
apparently Rails does not do appropriate conversion. We should just make
sure that the method to calculate the Total header returns a String.
This fixes #6

Signed-off-by: David Celis <me@davidcel.is>

Author: davidcelis

lib/api-pagination.rb

@@ -33,8 +33,8 @@ def pages_from(collection)
 
     def total_from(collection)
       case ApiPagination.paginator
-        when :kaminari      then collection.total_count
-        when :will_paginate then collection.total_entries
+        when :kaminari      then collection.total_count.to_s
+        when :will_paginate then collection.total_entries.to_s
       end
     end
   end