Move default_params dict update to relevant spot

[michaelhelmick]

https://github.com/michaelhelmick/python-mailsnake/blob/master/mailsnake/mailsnake.py#L51

to underneath https://github.com/michaelhelmick/python-mailsnake/blob/master/mailsnake/mailsnake.py#L40

[brad]

I think it needs to be where it is. If you moved it to under line 40, line 42 could overwrite it.