Fix UnicodeDecodeError

[tatterdemalion]

If params contain non-ascii characters merging fails.

[aaugustin]

This pull request shifts the problem but doesn't really solve it.

If SECRET_KEY is unicode (for instance because the settings module has from __future__ import unicode_literals) the same problem will still occur.

That said, it's a valid bug.

[Fak3]

maybe this will be better:

    params = force_text(settings.SECRET_KEY) + data['sql'].decode('ascii', 'replace') + data['params'].decode('ascii', 'replace')

[fedosov]

👍