flask: migrate报 Target database is not up to date.

一，报错信息：

ERROR [flask_migrate] Error: Target database is not up to date.

二，原因:

heads和current不一致

$ flask db heads
81c8f6bda7e0 (head)
$ flask db current
f8901f58fe37

三，解决:

$ flask db stamp head
$ flask db migrate
$ flask db upgrade