Use album_title field as title.

Not sure if Bandcamp changed their API or what, but my downloads do not
have a "title" field in them, causing the tool to loop endlessly through
all purchases and not download anything; this change fixes said problem
for me, but I saw that the response also includes keys such as
"item_title", which might be a more robust choice.

bandcampsync/bandcamp.py

@@ -211,7 +211,7 @@ def load_purchases(self):
                     log.error(f'Failed to locate band name in item metadata, skipping item...')
                     continue
                 try:
-                    title = item_data['title']
+                    title = item_data['album_title']
                 except KeyError:
                     log.error(f'Failed to locate title in item metadata (possibly a subscription?) for "{band_name}", skipping item...')
                     continue