fix: use chat_completion instead of completion when parsing .ask as it uses the chat endpoint (#54)

Author: mengqing

lib/langchainrb_rails/active_record/hooks.rb

@@ -117,7 +117,7 @@ def ask(question, k: 4, &block)
             question: question,
             k: k,
             &block
-          ).completion
+          ).chat_completion
         end
       end
     end