fix migration script

so that it uses the right verson of the model

ippisite/ippidb/migrations/0063_fill_drugbank_links.py

@@ -3,13 +3,13 @@
 from django.db import migrations, models
 import django.db.models.deletion
 
-from ippidb.models import Compound, DrugBankCompound
-
 def run_generate_drugbank_inchikey(apps, schema_editor):
+    DrugBankCompound = apps.get_model("ippidb", "DrugBankCompound")
     for drugbank_compound in DrugBankCompound.objects.all():
         drugbank_compound.save(autofill=True)
 
 def set_compound_drugbank_links(apps, schema_editor):
+    Compound = apps.get_model("ippidb", "Compound")
     for compound in Compound.objects.all():
         compound.set_drugbank_link()
         compound.save()