update granian worker count

Procfile

@@ -1,2 +1,2 @@
-web: python manage.py migrate --noinput && python manage.py clearcache && python manage.py collectstatic --noinput && granian --interface wsgi config.wsgi:application --workers 4 --host 0.0.0.0 --port $PORT
+web: python manage.py migrate --noinput && python manage.py clearcache && python manage.py collectstatic --noinput && granian --interface wsgi config.wsgi:application --workers 2 --host 0.0.0.0 --port $PORT
 worker: celery  -A config worker -l info