rename_field doesn't work

[cvitan]

The rename_field method fails with a KeyError on trying to get the old field from model._meta_fields, i.e. field = model._meta.fields[old_name]. As far as I can see, this will always fail since the model field has been renamed already and the old field name key is gone, or am I missing something?

Version: 1.0.0

Steps to reproduce:

1. rename the field of a model
2. create a migration that includes migrator.rename_field(FooModel, 'old_foo', 'new_bar')
3. run the migration

Expected: Success
Actual: the following exception:

  File "/usr/local/lib/python3.6/site-packages/peewee_migrate/migrator.py", line 260, in rename_column
    field = model._meta.fields[old_name]
KeyError: 'old_foo'