events app unit test

[SivanYeh]

Please help add unittests to API /api/events:

• schedule
• keynotes
• speeches
• speeches//
• speeches/category/ (check if it has already covered) code: https://github.com/pycontw/pycon.tw/tree/master/src/events unittest: https://github.com/pycontw/pycon.tw/tree/master/src/events/tests/api