IntegrityError: Problem installing fixture
It looks like you've generated fixtures that include Django's default data set, i.e. the built-in entries that are inserted normally as part of the first migrate run for some of Django's plumbing data types.
You should review your fixture process, because content type entries will be created automatically when your (and Django's) apps' migrations are run, so they should not be present in fixtures. It's possible there are other tables that will have this same problem, so now would be a good time to make sure you're not including any other data that would result in this situation.
I upload my first Django-project into DigitalOcean. After command python manage.py loaddata initial_data.json, I have received this message:

django.db.utils.IntegrityError: Problem installing fixture
  '/webapps/django_shop/shop/initial_data.json': Could not load
  contenttypes.ContentType(pk=3): duplicate key value violates unique
  constraint "django_content_type_app_label_76bd3d3b_uniq" DETAIL:  Key
  (app_label, model)=(auth, permission) already exists.

How can I fix it?