Update README.md

Author: ttt733

README.md

@@ -49,7 +49,7 @@ follows.
 
 The base URL for API calls defaults to `https://api.alpaca.markets/`. This endpoint
 is for live trading. You can change the base URL to `https://paper-api.alpaca.markets`
-for paper trading. You can specify the API URL with the environment variable, `APCA_API_BASE_URL`.
+for paper trading. You can specify the API URL with the environment variable `APCA_API_BASE_URL`.
 
 The environment variable `APCA_API_DATA_URL` can also be changed to configure the
 endpoint for returning data from the `/bars` endpoint. By default, it will use