[Answer]-Heroku postgis makemigrations error geodjango

Ok so I fixed this by enabling postgis on heroku by running these commands

heroku pg:psql
create extension postgis;

then I ran this command to see what version i had on heroku

SELECT PostGIS_full_version();

then I put this is my settings.py file

POSTGIS_VERSION = (2, 1, 5)

and viola it works!