[FIX] Fixed incorrect filename to class inflection in Rake import task

`bundle exec rake environment tire:import:all` now succeeds for a `Address` model.

Fix provided by @congshuanglong.

Closes #733, closes #744

lib/tire/tasks.rb

@@ -134,7 +134,7 @@ def import_model(index, klass, params)
         require path
 
         model_filename = path[/#{Regexp.escape(dir.to_s)}\/([^\.]+).rb/, 1]
-        klass          = model_filename.classify.constantize
+        klass          = model_filename.camelize.constantize
 
         # Skip if the class doesn't have Tire integration
         next unless klass.respond_to?(:tire)