Merge branch 'check/update-tox-ini' into 'master'

aleksis/apps/untis/management/commands/untis_import_mysql.py

aleksis/apps/untis/util/mysql/importers/absences.py

aleksis/apps/untis/util/mysql/importers/common_data.py

aleksis/apps/untis/util/mysql/importers/events.py

aleksis/apps/untis/util/mysql/importers/exams.py

aleksis/apps/untis/util/mysql/importers/holidays.py

aleksis/apps/untis/util/mysql/importers/lessons.py

aleksis/apps/untis/util/mysql/importers/substitutions.py

aleksis/apps/untis/util/mysql/importers/terms.py

aleksis/apps/untis/util/mysql/main.py

aleksis/apps/untis/util/mysql/util.py

tox.ini