Merge pull request #5 from y-yagi/fix_ruby_warning

Fix ruby warning

lib/yuba/rendering.rb

@@ -17,7 +17,7 @@ def _protected_ivars
     end
 
     def view_model_assigns
-      return {} unless @_view_model
+      return {} unless defined?(@_view_model)
       # TODO: get all public methods between self and Yuba::ViewModel
       #       now get only in self
       methods = @_view_model.public_methods(false)