[doc] Fix trailing comma in S3MediaStorage section (#438)

Co-authored-by: Daniel Townsend <[email protected]>

Author: Compro-Prasad

docs/source/media_storage/index.rst

@@ -216,17 +216,17 @@ In order to associate a column with ``S3MediaStorage``, we do the following:
 
     MOVIE_POSTER_MEDIA = S3MediaStorage(
         column=Movie.poster,
-        bucket_name="bucket123"
-        folder_name="movie_poster"
+        bucket_name="bucket123",
+        folder_name="movie_poster",
         connection_kwargs=S3_CONNECTION_KWARGS,
         allowed_extensions=['jpg', 'jpeg', 'png']
     )
 
 
     MOVIE_SCREENSHOTS_MEDIA = S3MediaStorage(
         column=Movie.screenshots,
-        bucket_name="bucket123"
-        folder_name="movie_screenshots"
+        bucket_name="bucket123",
+        folder_name="movie_screenshots",
         connection_kwargs=S3_CONNECTION_KWARGS,
         allowed_extensions=['jpg', 'jpeg', 'png']
     )