Update config.json

Author: buddyuchiha

config.json

@@ -5,10 +5,10 @@
     "tester": "foobar123"
   },
   "db_config": {
-    "host": "localhost",
+    "host": "db",
     "port": 3306,
     "user": "root",
     "password": "mypass",
     "database": "catty_reminders"
   }
-}
+}