add default SECRET_KEY to test suite (#204)
add default SECRET_KEY to test suite (#204)

https://github.com/django/django/pull/9876 removed the default
SECRET_KEY, leading to an error when we try to access it in the
tests

closes #204

beniwohli/apm-agent-python,beniwohli/apm-agent-python,beniwohli/apm-agent-python,beniwohli/apm-agent-python