## Bug description
- See screenshot below (it's likely being processed in 3 workers at the same time).

![sc](https://user-images.githubusercontent.com/5864173/92016443-f6457800-ed17-11ea-9b7f-959a3306850e.png)


## Expected behavior
- We should receive the event only once.


## How to reproduce

1. View a user of recent creation with this event ([example](https://app.posthog.com/person/5fabb7b9-a36c-4419-af97-eea75960b2e4)) 

## Environment

- Cloud from PR #1508 

#### *Thank you* for your bug report – we love squashing them!

posthog/celery.py
import os
import time
import statsd
from celery import Celery
from celery.schedules import crontab
from django.conf import settings
from django.db import connection
from django.utils import timezone
from posthog.ee import check_ee_enabled
from posthog.redis import get_client
os.environ.setdefault("DJANGO_SETTINGS_MODULE", "posthog.settings")
app = Celery("posthog")
app.config_from_object("django.conf:settings", namespace="CELERY")
app.autodiscover_tasks()
app.conf.broker_pool_limit = 0
ACTION_EVENT_MAPPING_INTERVAL_MINUTES = 10
statsd.Connection.set_defaults(host=settings.STATSD_HOST, port=settings.STATSD_PORT)
@app.on_after_configure.connect
def setup_periodic_tasks(sender, **kwargs):