fix env var ref

app.py

@@ -51,7 +51,7 @@ Context:
 """
 text_splitter = RecursiveCharacterTextSplitter(chunk_size=1000, chunk_overlap=100)
 hf_llm = HuggingFaceEndpoint(
-    endpoint_url=f"{os.environ["YOUR_LLM_ENDPOINT_URL"]}",
+    endpoint_url=os.environ["YOUR_LLM_ENDPOINT_URL"],
     max_new_tokens=512,
     top_k=10,
     top_p=0.95,