fix syntax error

app.py

@@ -261,7 +261,7 @@ def main():
         st.session_state.auto_submit_text = text
 
     # Accept user input
-    prompt = st.chat_input("Type your claim here"):
+    prompt = st.chat_input("Type your claim here")
     if prompt:
         # Add user message to chat history
         display_message = prompt + "  \n"+ "  \n"+ f"Retriever: {selected_retriever}, Reasoner: {selected_reasoner}"