Changed django-model-utils dependency version to be the latest version on PyPi that contains InheritanceManager.
Changed django-model-utils dependency version to be the latest version on PyPi that contains InheritanceManager.

The TravisCI build was having trouble installing this dependency with PyPi when the version was set to 'tip'.

denverfoundation/storybase,denverfoundation/storybase,denverfoundation/storybase,denverfoundation/storybase