fix: typo in comment (#621)

Author: terezapohankova

src/dotenv/main.py

@@ -403,7 +403,7 @@ def load_dotenv(
         Bool: True if at least one environment variable is set else False
 
     If both `dotenv_path` and `stream` are `None`, `find_dotenv()` is used to find the
-    .env file with it's default parameters. If you need to change the default parameters
+    .env file with its default parameters. If you need to change the default parameters
     of `find_dotenv()`, you can explicitly call `find_dotenv()` and pass the result
     to this function as `dotenv_path`.