Logical statement on line 57 of sandman2/__init__.py, replaced 'if' with...

Logical error on *line 57* of `sandman2/__init__.py`, replaced `if` with `elif`.  

`sandman_model` returned to *line 150* of `sandman2/__init__.py`.  *Line 151* updated accordingly.  Not sure what the reason for changing this was previously.  

I feel a tad silly making a pull request for such a small contribution.  However, upon finding this project both TravisCI and myself agreed that the tests weren't passing.  These changes make all tests pass for me.