corrected openai_api_key param typo

app.py

@@ -57,7 +57,7 @@ def loading_pdf():
 def loading_database(open_ai_key):
     if open_ai_key is not None:
         if os.path.exists(PERSIST_DIRECTORY):
-            embeddings = OpenAIEmbeddings(open_ai_key=open_ai_key)
+            embeddings = OpenAIEmbeddings(openai_api_key=open_ai_key)
             docs_retriever = Chroma(persist_directory=PERSIST_DIRECTORY, embedding_function=embeddings)
 
             global qa_chain