PHP 7.2 incompatibility

[Vektor75]

I've installed on my dev laptop the PHP7.2 version, and it required to update yii2 to version 2.0.13 at least. And because of this workflow-manager has broken.

I suggest to create a branch for PHP7.2 compatibility with the following changes:

in the vendor\cornernote\yii2-workflow-manager\src\components\WorkflowDbSource.php file
change line 15
from this
use yii\base\Object;
to this
use yii\base\BaseObject;

and change line 35
from
class WorkflowDbSource extends Object implements IWorkflowSource
to the following
class WorkflowDbSource extends BaseObject implements IWorkflowSource

and that's it, after this small changes the extension is working without any errors