migration for guild ID change

src/db.py

@@ -90,6 +90,13 @@ CREATE TABLE discord_webhooks (
     channel_id INTEGER PRIMARY KEY,
     webhook TEXT NOT NULL
 );
+""",
+"""
+UPDATE user_data SET guild_id = '_global' WHERE rowid IN 
+(SELECT 
+    (SELECT rowid FROM user_data d WHERE d.key = user_data.key AND d.user_id = user_data.user_id ORDER BY rowid DESC LIMIT 1) 
+    FROM user_data WHERE guild_id IS NULL GROUP BY user_id, key);
+DELETE FROM user_data WHERE guild_id IS NULL;
 """
 ]