fixed another typo

index.html

@@ -20,7 +20,7 @@
 		const textbox = document.querySelector("#prompt")
 		const res = document.querySelector("#response")
 		const prompt = textbox.value 
-		btn.on("click", event => {
+		btn.addEventListener("click", event => {
 			fetch(`/gpt?prompt=${prompt}`)
 				.then(res => res.json())
 				.then(res => {