Fix string only parameter in $.toaster call

[isaac-jordan]

The $.toaster function only checks for whether the incoming parameter is an object. In the Usage section of the README it mentions that a string can be passed to use default values.
I have implemented this small change.

Section from README:
/*

• ...or pass only a string; it will be treated as the intended message,
• and 'priority' will default to 'success', and 'title' to 'Notice'.
  */
  $.toaster('Whatever you did worked!');