Log Message:
py-django-filer: updated to 1.4.0

1.4.0:
* Added support for Django 2.0 and 2.1
* Enabled django-mptt 0.9
* Converted QueryDict to dict before manipulating in admin
* Hide 'Save as new' button in file admin
* Fixed history link for folder and image object
* Fixed rendering canonical URL in change form