Fix on Pgvector#ask (#39)

* Update pgvector.rb

Fix on `Pgvector#ask` that uses the wrong syntax of `llm.chat`

* Linting error fix on pgvector.rb

Space inside { detected on line 120.

Fix space inside for:
```
 messages = [{ role: "user", content: prompt }]
```

Author: iamademar

lib/langchainrb_overrides/vectorsearch/pgvector.rb

@@ -117,7 +117,8 @@ def ask(question:, k: 4, &block)
 
         prompt = generate_rag_prompt(question: question, context: context)
 
-        llm.chat(prompt: prompt, &block)
+        messages = [{role: "user", content: prompt}]
+        llm.chat(messages: messages, &block)
       end
     end
   end