heroku部署flask失败

Question

按照狗书的代码，成功将程序 push 到 heroku master ，结果运行 heroku run python flasky.py deploy 失败
报错如下：
File "/app/.heroku/python/lib/python3.6/site-packages/alembic/script/base.py", line 334, in _upgrade_revs

revs = list(revs)

File "/app/.heroku/python/lib/python3.6/site-packages/alembic/script/revision.py", line 652, in _iterate_revisions

uppers = util.dedupe_tuple(self.get_revisions(upper))

File "/app/.heroku/python/lib/python3.6/site-packages/alembic/script/revision.py", line 300, in get_revisions

resolved_id, branch_label = self._resolve_revision_number(id_)

File "/app/.heroku/python/lib/python3.6/site-packages/alembic/script/revision.py", line 433, in _resolve_revision_number

self._revision_map

File "/app/.heroku/python/lib/python3.6/site-packages/alembic/util/langhelpers.py", line 240, in get

obj.__dict__[self.__name__] = result = self.fget(obj)

File "/app/.heroku/python/lib/python3.6/site-packages/alembic/script/revision.py", line 121, in _revision_map

for revision in self._generator():

File "/app/.heroku/python/lib/python3.6/site-packages/alembic/script/base.py", line 90, in _load_revisions

for file_ in os.listdir(vers):

FileNotFoundError: [Errno 2] No such file or directory: '/app/migrations/versions'
只截了一部分，太长了，求大神指点