docs: fix safePrompt on JS Guardrailing

Author: RemiSaurel

docs/capabilities/guardrailing.mdx

@@ -26,7 +26,7 @@ chat_response = client.chat(
 const chatResponse = await client.chat(
     model: 'mistral-large-latest',
     messages: [{role: 'user', content: 'What is the best French cheese?'}],
-    safe_prompt: true
+    safePrompt: true
 );
 ```
   </TabItem>