Update MY_Model.php

update_where for multiple field
Merge pull request #922 from vachzar/patch-1

Update MY_Model to support multiple fields in the update_where command. At some point, we need to make sure all of the methods take multiple options.
Update MY_Model.php

fix little typo
Merge pull request #923 from vachzar/patch-2

Update MY_Model.php