Update requirements and update Elasticsearch to version 6

openlobby/core/documents.py

openlobby/settings.py

requirements.in

requirements.txt

tests/mutations/snapshots/snap_test_create_report.py

tests/mutations/snapshots/snap_test_update_report.py

tests/schema/snapshots/snap_test_authors.py

tests/schema/snapshots/snap_test_search_reports.py