fixing app.py

app.py

@@ -77,7 +77,7 @@ def main():
         st.write("### Please wait while we are getting the answer.....")                                                                                 
         llm = ChatNVIDIA(
             model=READER_MODEL_NAME,
-            api_key= os.get("NVIDIA_API_KEY"), 
+            api_key= os.getenv("NVIDIA_API_KEY"), 
             temperature=0.2,
             top_p=0.7,
             max_tokens=1024,